I can provide at least a partial answer:
1. For at least some of those things, you'd be able to see online if a secondary card would have been issued - and at least some of those that were offered won't let secondary cards be issued without disabling any previously issued cards, so either your card would already be dead or the other guy's card would be dead.
2. Seller mentions in this thread that he bought these from people who worked in the EU and used them to receive wages, but no longer had use for them when they left or whatever... whether that's true or not, I don't know, but that was what the seller mentioned.
3. If you deposit money on it, then that inadvertantly implies that you are the one with the live card, see part 1 of my comment, so at least in some of the cases any previous owner would not be able to just get to the money you deposited.
In the case of Skrill, at least, there is a bit of a snag I think... with Skrill they might be able to try and take the accounts back, but most likely that'd result in Skrill freezing the account for investigation, so neither you nor the previous card owner would be able to get to the money.
If the previous owner is in another country than where they opened the Skrill from, and you are on an IP close enough to match the right country, then there's a bit more chance that Skrill considers you to be the legit owner, though there'd also have to be the security questions and stuff - and you'd probably need to have access to the original email to change password/security questions.

I don't know about the actual bank cards, I never messed with those myself... maybe something I should try out, just for educational purposes... hm... then again, I don't like the thought of possibly messing it up and becoming inmate 74758's new prison bride :p
Gah, no guts no glory, I'll just do some careful research before deciding...

Edit, because I forgot something:
To the one asking about how the cards could be used if the names do not match; seller already answered, but I'll add that it can be a hit-or-miss situation.
Some banks do check, some don't, and some do randomly/sporadically but not all the time.
I know at least one time, where I worked for a temp agency which messed up... they sent my wages, with my name, to the wrong bank account; the owner of that bank account never replied to anything, my own bank couldn't just get it, the temp agency's bank tried to retrieve the money but couldn't because the other guy already cleaned his account out and never replied to anything... pretty much I was left holding the bag on that situaton, and it was a paper bag, with a flaming turd in it.
But I've also heard of other banks that do things differently, that will check everything in detail all the time, and some that do sporadic checks.
The bank I'm with now is one of those that don't always check, but still do check plenty of times to make it risky enough for anyone trying to mess with such things.