Auction or main fleet? Mon - Fri or 4 on 4 off?
Wages differ week to week depending on work but if you’re on main fleet and out Mon-Fri and when you’re up to speed (which could take 6 months to a year depending on how you take to it) then generally £750 - 800 take home atm. If you want to make that then you’ll be doing 55-60 hrs every week and earning every penny and some. You don’t get deductions for damaging cars but there is a damage bonus and there’s only so much damage they’ll put up with.
Conditions - it’s a tough job. You’ll work twice as hard as the rest of the industry for probably no better money hence lots leaving. New car work is slow since covid and no signs of it picking up so lots of multi-drop and auction work which doesn’t pay as well, so take home pay has gone down in reality while the rest of the haulage industry has had a pay rise 
If it’s something that you want to do, then go for it. BCA are no better or worse than anyone else to work for, the training is good. If you are only interested because you think it’s mega money, then I wouldn’t bother, it’s just not the case any more!