Thanks all for the opinions.
Mrs A still pi**ed off, but I have promised to try and find a similar (or better) equivalent. trouble is, the one she wanted had a ton of extras that I haven't seen on any other car.
Mr & Mrs B, however, over the moon and we have two nice px's to sell.
I agree with pretty much everything you say, although we employ a couple of slightly different tactics especially with regard to 'holding deposits'
We never, never just hold a vehicle whilst someone makes their mind up. As Chris said, why leave ourselves open to the possibility of losing a sale twice? If, however, someone is travelling a fair distance to see a car, I will take it off sale for them, if they ring when they are leaving, until they arrive.
Deposits are £500 minimum - creates obligation and stops them shopping around after agreeing to buy ours. If they ask if deposits are refundable, it is obvious that they are not obligated and therefore more needs to be done to get over the line.