Is an iphone 5 16GB (AT&T unlocked) worth 350$?

Is an iphone 5 (AT&T unlocked) worth 350$?
I just bought one off ebay, it's really clean, like no wear at all. The guy at Tmobile says I should have gotten a 5s for the price I paid. Now I'm reconsidering the "good deal" I just got in the mail. What would you say? I upgraded from the iphone 4.

How much will an Iphone 5s cost even if I already have a contract with Verizon?

Okay, so, I've had the same phone (the Iphone 4) since 2012, and I think it's time for a change. Now, on top of being time for a change, my screen is cracked and the home button rarely ever works. However, I already have a two year contract with Verizon, which has been renewed recently, and I don't currently have a free upgrade. If someone that knows the answer could share their knowledge it would be very appreciated, thank you!

What is a trade-in credit? At&t?

This is what is says basically "Trade-in Value: $300 value for iPhone 5s and $200 value for other eligible iPhones. In AT&T-owned retail stores trade-in will instantly receive value as a private label AT&T "

So i don't understand at all. If i turn in my barely scratched iphone 5s, i will get $300 as in cash or into my credit card. That means i will be $300 richer, in my hand or in my bank? I want to buy a iphone6, $200, so i will save $100 without spending a cent on the iphone6 just by returning my 5s to them?