Try
1-Grand Sterling on 13th ave, and
2-Prime Sterling on 18th ave in BP
3-AB Silver on 49th street as well, and
4-Theres a silver repair place, a Mr Levy, I think 5205 13th ave on top of Kodesh religious articles, (or next door).
These places buy old silver. See who offers you more. I think theyre all pretty honest (but will try to pay as little as possible) which is why you’d want to go to a few places. Thats easy because theyre all pretty close to one another.
As far as distinguishing silver plate from solid silver, items would be marked 800 or 925 or sterling if theyre not silverplate.