In general, I preferred to buy from sellers who used eBay to sell personal possessions from home that they no longer had use for. Of course, you want to buy from a person who has enough feedback on transactions that you can see that they have a history of being trustworthy. I mostly steered clear of people who sold a lot of phones or electronics items as they were clearly selling professionally and it was hard to have confidence in the history of those phones. A majority of the used phones being sold on eBay are by refurbishers and repairers or lost/stolen devices.
There is nothing wrong with buying from a refurbishers who has excellent feedback but the problem is what many sellers often don't say in their posts that the average person doesn't know about. If one of your selling points for buying an iPhone 7 Plus was the camera quality and the refurbisher actually replaced that camera with a non-OEM camera with worse clarity and functionality wouldn't you want to know about it. It happens. I think most refurbishers use cheaper parts because they don't think it will really warrant a higher selling price to use OEM parts and they simply want a bigger profit.
First of all, if you are going to buy from a refurbisher or selller make sure they have near 100% positive feedback. I'm talking 99% or above. Of course, a seller can get a jerk buyer who leaves bad feedback for a terrible reason, but I was actually surprised by how understanding most people are. For most people, if the seller at least tries to make it right, then they will refrain from leaving negative feedback (I know because I have made a numerous dumb mistakes).
Second, if the refurbisher doesn't say in their listing whether or not the refurbishing was done using OEM parts then ask them in a message. There are some people who will lie to you, but for the most part, the people who make a living at it don't want the hassle of going through a return and eBay forcing them to pay return shipping and taking a chance of negative feedback if the customer turns out to be knowledgeable and looks into it when they get the phone. Which is another good reason to pick a seller with excellent feedback, because they will want to protect that feedback score and do what's right. The guy who already has only 90% positive feedback probably didn't care in the past and he is already low and is likely not going to lose sleep over a little more negative feedback.
Third, get great pictures. If they have terrible pictures, with low resolution, taken from far away, with bad lighting and they only show a couple angles of the phone.... there is probably a reason for that. If you have a phone in perfect condition that you want to sell then you try to capture that in your pictures. You wll be able to demand a higher price for it. If they say it is in excellent condition but don't have the pictures to back it up, then ask for more. People who have nothing to hide will provide them because they want to make the sale.
On that same note, look for pictures of the screen on. First of all, you want to ensure that the phone is actually functioning. Second, you want to see any defects that there might be on the screen (such as light spots, or dark spots, lines, black areas, etc.). Last and most importantly, you want to see that the seller has access to the phone. If the only screen they have posted is of the "Hello" setup introduction screen or any of the screens leading up to the Activation screen during setup (for iPhones, but a similar line of thinking applies to other phones), then I would ask to see it fully setup. This is a good way to mostly guarantee you aren't getting an activation locked phone.
The same can be said if you are buying from the original owner of a phone. You should probably ask if the screen or any other components have ever been replaced and ask for good pictures from those who claim to be the original owner as well.
Also, don't ever buy a really expensive item from a person with little to no selling history. It might be very tempting because the price is usually much lower, but there is a reason for that. Experienced eBayers know to stay away from those listings and so there are much fewer people bidding on those items. These can be scammers or an individual trying to sell a stolen item. They sign up for a new eBay account with a new fake email and make their sale and cancel it as soon as they can withdraw the money from Paypal. You might get the item and think everything is great and not realize there is a problem with the phone until quite some time later. Then that person is already gone. It is my understanding that eBay will give the buyers money back for transactions like these but it eats up a lot of your time and is exhausting.
I have very little experience with Swappa, as I only bought damaged phones for refurbishing and Swappa requires that phones are completely functional, without damage that requires repair. I did visit the site somewhat frequently to gauge pricing trends, however. In general, I think that Swappa prices are a little bit higher than I would see on eBay when considering all the variables that determine a phones worth. I do think that buyers have more protection on Swappa, however. It is my understanding that Swappa will verify a phones IMEI status before it can be posted, which is a big deal. All that being said, I would still contact sellers if possible and inquire about the phones repair history. There are a lot of refurbishers selling on Swappa as well, and I'm sure it’s the same M.O. Profit.
Lastly, watch out for scammers. There are many scammers out there trying to get people to ship without actually receiving funds, so I'm sure there are plenty out there trying to get people to send them money outside of Paypal and whatever other stuff they can come up with. Don't do it. It's not worth the risk. There are a lot of people who make a living off of eBay scams.
Hope I provided someone out there with some useful information.
Once you do receive the phone make sure that it the same phone as in the listing by comparing IMEI numbers (assuming you got it before purchasing). Also, check over the functionality and make sure the phone is as described by the seller. I have an earlier blog post on what items to check off if you are unsure. Once your phone is setup there are some great free apps that you can download from the App store that make it very easy to check out the functionality of your device. TestM is a really good one.
One last note. Sometimes you can be so excited to get that new phone that your reason is a little clouded. Be mindful of your thoughts. They will betray you. There are plenty of phones in the sea.... or rather the internet. Let someone else take risks with their hundreds of dollars. Just be smart, do your work, be a bit cautious and have patience and you should find a great phone for a great price.
If you are fuzzy on anything I said or have any question please feel free to message me and I would love to help (and know someone actually read this haha). Until next time.
May the Force be with you. And peace and grace as well.
Jeff - Tech Jedi - Quality Device Repairs