The only (tiny) risk with a bankers draft is either it not being made out properly (clerical error at bank) OR
(more of an issue) if it is stolen, this occasionally happens in bank raids. It won't clear any quicker than a normal cheque but as the chap is debited for it when it is issued, there isn't a risk of it being returned for lack of funds, essentially he buys the draft from the bank.
The draft should be issued from the bank itself, they are normally quite a bit bigger than a normal cheque. As well as the amount in writing and in the figures box, there's a diagonal line across in which the clerk writes 'not more than and then puts an amount 1p more than the amount of the draft - to stop additions or alterations).
So provided all this is complete and it's signed, in my old bank it was 2 signatures, that should be fine on the completeness front.
Re stolen drafts, what you need to do is to ask the buyer to ring you once the draft has been issued, they will have to collect it beforehand so this will probably be Friday, to give you all the serial numbers and bank branch details on the draft - and you need to know this info so you can ring up still in banking hours and confirm with that branch of that bank that the draft is genuine and not counterfeit or stolen.
Hope this helps :-)))