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.
You might have the live card but the owner does not need the card to use it online; he just needs the numbers on the card, which could have been prerecorded before selling the card to you.
Again, look at part 1; I know you have, but just for reference:
...
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.
...
The bold, italic part, that implies you having access to the online thing.
And that's where you can also fix/tinker with/combobulate/dissemminate/alter/go Freddy Krueger on stuff like passwords and whatnot.
Granted, it won't be that easy or even possible for all those online banking things/Skrills/whatnots, but there'd still be a wealth of info in there.
Previous owner logged in just two days ago?
You'd be seeing that, and know that chances are he's waiting to bamboozle you internet-style.
Previous owner's last log-in was weeks or months ago?
Less chance of him pulling a fast one on you.
If you're willing to take the word of any bank clerk that your money is 100% safe in that bank, then you can do the same for any other person selling stuff or services... because the only way to have 100% guarantee in money matters, is to close your eyes and imagine getting that big lottery prize - unfortunately, while getting it that way is a 100% guarantee, it's kind of hard to spend those lottery winnings anywhere in the real world...
Even the baker can give "only" 99.999999% guarantee that his bread will not kill you, and he'd still be taking a gamble of a few percent on that, an educated guess-type gamble based on his previous experiences, at best.
At worst, he's that mass murderer who hasn't been caught yet, and that's no almond in that almond-flavored pecan pie he just made you taste a slice from... yeah, I joke about that in an over-exhaggerated way, but unless you and the baker and the bank clerk came from that same womb, went to the same school, and celebrated all your birthdays together, chances are you don't know them well enough to trust that their 100% guarantees are really 100% honest.
And now that I've made you put on a tinfoil hat whenever you go for groceries, I'll repeat the point; if you can see online that no second card was issued or any other funky stuff went on, then chances are that you tinker with the password as well... though in my earlier statement about that I forgot to add that you'd probably need the email address for that, too... or convince them that you as uh... the uh... legit owner no longer have access to that email address.
Not very common, but not entirely uncommon either, people do lose email addresses and even switch providers without thinking that they might need that stuff for the bank.
Edit for buybtc1 - I tried replying to that pm, but it said I was trying to soon.
I'll go do some groceries (takes me between 30 minutes and an hour) and then I'll send my reply.