Can you trade in an iPhone 5s at an Apple Store and if possible how much is it?

I'm planning to trade in my iPhone 5s at an Apple Store to lower the cost for an iPhone 7+. I want to know if it's possible to trade my 5s in and how much it would be if I could.

Apple does not buy in your obsolete gear as a trade-in.

If you want to know what your phone sells for then eBay is an excellent guide: enter the exact model, colour, storage capacity and then use the "sold items" filter. As you look through the results you'll still see some variation according to whether the phone is in excellent condition or not. Boxed and near-mint with all original accessories fetches the highest price. If the phone is factory unlocked to all networks it's worth more than one which is tied to any particular network.

The prices you'll se are what private buyers will pay. Used electronics shops will pay you far less because they have the costs of running a shop, checking and guaranteeing what they buy for resale, and must make a profit as well. But they do pay straight away (you must show proofs of your I.D. And address) in contrast to private sales where some buyers will try to defraud the seller.

Prices vary worldwide so it's not even possible to suggest a very approximate price range as you've failed to state where you live.

In short, if you want to know for definite what you'll be paid then take the phone to a used electronics store such as CEX (there are many others) and ask them for a quotation. They will need to keep and test the phone for around an hour to check for faults. But unless you do your research in advance you won't know whether the offer is a fair one or not.