Such as,
setid = setid
local info = game:GetService("MarketplaceService"):GetProductInfo(setid)
print(info.Name)
GetProductInfo only works for assets (hats, models, gear, etc) and developer products. Sets are a totally different type of thing.
There are some methods in InsertService that let you fetch information about a user's sets: http://wiki.roblox.com/index.php?title=InsertService