I'm considering buying a used samsung fascinate from an ebay power-seller. they say that it runs fine' but that it doesn't allow any apps to be run.
can this be fixed with a root and custom ROM, or some other fix, or is it a lost cause
That could go either way. I would say it is probably fixable, but with out actually seeing the phone it hard to say. See if you can get more details.
Sounds like Voodoo - zero internal memory. If that's it, it's a quick fix.
Can't you just buy it, activate it and return it to Verizon for a warranty replacement?