Best phone to buy to trade in for new Galaxy

[JuryDuty]

I want to buy the new galaxy with the promotion of trade in s that Dan posted. I figure if I can buy a used phone and trade it in, I can save some serious cash. Any ideas for the best way to take advantage?
https://www.dansdeals.com/shopping-deals/electronics/cell-phones/order-galaxy-s10-s10-today-receive-130-accessories-credit-plus-get-s10-low-349-99-550-off-trade-credit/

[myi]

Go to swappa.com and buy a phone like this or search through all the eligible phones to see which one you can get for the best price and which is in the best condition so you get the best bang for your buck for example this phone you can make $200 off.
https://swappa.com/listing/view/LRQG24475
this phone is in good condition and most probably will qualify for the $200 or rather $550 which you'll make only $200 profit.

So it would come out to around $650 with $130 credit.
  I wonder what the going price would be on swappa once these phones are released.
 I would buy to flip if I know I can get $750 plus.

[JuryDuty]

The v40 that samsung refers to is the ThinQ? Is that the only v40? On ebay it looks cheaper

[myi]

The v40 that samsung refers to is the ThinQ? Is that the only v40? On ebay it looks cheaper

I think it means the same thing but don't rely on me just assuming.
yes you can buy from wherever just the products I bought from swappa in the past was much better than what you find an eBay but yes look through the listing see the condition and if it makes sense then buy from eBay.