Making an enquiry never makes sense to me either.
How do you do it?
Can we ask you if we can ask if you'll sell a player to us?
It's like one of the two most pointless questions ever asked 'can I ask you a question?'
The other one, btw, is 'are you awake?'
If you make a bid and it's accepted you've got a contract, which can be enforced. But if you don't have the money to back up that bid you're fucked.
If you make an enquiry to see what the parameters of a deal might be - you haven't put yourself under any obligation. Which suits if you need player x to be sold before you buy player y.