There are quite a few Plat Alloys out there depending, most is 950 or .900, and some is .585.
Refining platinum is expensive. Most small refiners and jewelers just melt it down to cast into a new piece, or fix it to sell again, you can melt it over and over with out refining in most cases.
First thing to get out of ones head is you will never be bale to see melt value out of something, unless your selling to someone who is going to use it as a wedding band.
Premiums are only paid on things that are new, or made to be new again.
I see time and time again people who sell scrap iron, scrap Al Cans or copper for half of melt value or less, but when it comes to gold or silver or platinum, they think they somehow can get melt? Fortunately there are suckers out there.
If you want to get top dollar put it on ebay, there are plenty of suckers out there that will pay close to melt just because they dont know, they dont know the alloys, they dont know squat. but they might get rich off it so they buy. If you have just one piece and you found it and want top dollar, Sell it too a sucker rather than a professional. This will get you more, and it becomes the suckers problem on...how to get rich of what he just over paid for.
thats my advice.