I think they should merge all the BF's into one massive online game. So like you start off with the original one and as you level up you go into the zones for the newer modern ones. And at the end you flashback in time to BF1!!! mwahah.
I miss playing BF3 sometimes.
But yea, all of mine from BF3, BF4, Hardline and all the premiums I have ordered from all the shady looking online key sites but have NEVER had issues.
The Division I ordered and had issues with but it was because they apparently typed the key wrong, after 24 hours they corrected and I was back in action.
Most these sites get these just by buying them in the cheaper countries and re-selling them since the games are generally global region. Once it's linked to your account you own it. It's VERY rare for a key to get blacklisted. Even all those stolen ones that ended up for far cry 4 I think they ended up ultimately letting people keep.
I refuse to pay full price!!! That and I'm a cheap poor bastard.