I've done transfers a fair times without taking payment first. I wouldn't anymore. IMO it's human nature to assume because you dont scam anybody, maybe they wont scam you, bad philosophy which I'm guilty of more than once.
It isn't just acorn members or other individuals you have to worry about, it's companies also. I had a DRS which I settled directly with the complainant (I can do without Nominets "mediation").
I agreed to sell the name to the complainant, email chain with complainants representative agreeing price etc, (Nominet legal team cc'd throughout.) Trying to demonstrate an act of good faith I done the transfer prior to accepting payment, bad idea with hindsight. Between the time I invoiced them and the company settling the invoice, the company went into administration. But only the company who was acting on behalf of the company who wanted the name went into adminsitration. The company who wanted the name got it having paid nothing for it.
Nominets reponse, let us check with our legal buffoons, I mean boffins ;-) and we'll get back to you. A week later, the answer is tough luck, we wont revert the transfer, go to the small claims court.
If I'd used escrow / insisted on payment up front there would have been no problem, so arguably the problem was of my own creation.