I would not use WBAB again after a bad experience some years ago. I was sellling a Harley worth around £10,000 and contacted them. I described the bike exactly as it was in every possible way and we agreed a price, on the perfectly reasonable understanding that it was correctly described. Chap turns up, takes a very brief look and offers me £1,000 under the agreed price. I asked him if it was exactly as I described and he agreed it was. Anything I hadn't disclosed? No he couldn't find anything because there was't anything. So I asked him why they dishonoured the agreement. "Just the way we work", he replied. "Scummy" I told him.
How they operate is that if they want the bike, they deliberately make an attractive agreed offer before the meeting, which they know they won't honour, in order to entice you in. Then when they arrive with the cash, they drop the price despite having agreed it earlier, hoping the owner may well accept the temptation of a lower cash offer on the spot to avoid further selling hassles elsewhere, and to hell with decency and honour. In the end I haggled and got him to raise the offer but it was still £500 lower than agreed, which I accepted precisely for the above reason. You can always refuse of course and I expect some do, and I expect also that many, as I did, reluctantly accept a lower figure, but either way it's a dirty trick.
If you do use them, never trust an "agreed" offer they make before turning up. It aint worth shit.