This is less legal advice and more moral advice, and you're not gong to like it.
You shouldn't take their money. More specifically there is no morally righteous justification - whatsoever - for you taking their money.
YOU (or rather your girlfriend) chose to do business and/or to continue to do business with a person whom you describe as "a fucking backstabbing bitch". You knew her. The potential new owners did not. You and your gf need to buck up and accept whatever consequences go along with doing business with such a person (rather than trying to pawn that responsibility off to someone else via threat of keeping their deposit) whether that means taking longer to sell your business or being forced to sell for a lower price.
If I understand what you wrote about "forcing" them to sign the contract to mean you're not even content to swallow their deposit but want to force them to complete a transaction they are not comfortable with - for apparently very good reasons - I find that absolutely unconscionable as well as absurd (no: nobody is going to force them to sign the contract or remit the other 3/4 payment).
If your GFs business were worth what she's selling it for than you wouldn't be worried about trying to force someone's hand - you'd just sell to the next buyer.
Very shady dealings here and one of the worst and most disappointing posts I've seen on expat-blog thus far.
Your integrity (and that of your GF) SHOULD be worth more to you than any dollar figure. JMHO.
Hi, I understand your post and appreciate it.
and I must admit, I wrote this in a moment when I was absolutely furious. I calmed down now.
I know we cannot force them to sign, this I miswrote. I also know from a moral point, its absolutely wrong to keep their deposit. We cant blame them in fact, and in a way they also understood us, and they also proposed to give gave back like 90% of the deposit. In a way this seems to be fair (because they already start working today, so they make some profit) so its fair they accept a little loss on their deposit. My gf also agreed with that, but I am the one who find it hard to swallow. Especially if you have some bad history with backstabbing, dishonest vietnamese. I know you dont have behave like them, but I hope you also undertand my anger.
This whole situation gave me a lot of stress and than on the day after my gf find someone who want to buy, and when I was thinking to leave this whole business story all behind, this happen. I dont have to say, today is an awful evening.
Offcourse I mostly anger and extremely disappointed in the owner of the coffeeshop. We try to be very sweet, friendly, but its already the second time in one week she scares a potential buyer away.