has anyone succesfully persuaded a vendor to rent instead?

[hatwoman]

if so how? any reasons not to try?

No reason not to try I suppose but generally people want to sell a house because they want/need the money tied up in it to buy a new one so I think you'd have limited success...

I would obviously speak via the estate agent and I see no reasons why you shouldn't try. I'm sure when I was working in an estate agents we were approached and on an odd occassion when the house had been on the market for a while it was successful.