My brain works like that as well but you're still sticking £7k on a 12/1 shot at the end of the day, the minute they offer you that cashback it's your money if you want it, in my day you didn't get the choice, I remember getting pipped for £12k when I was about 12,13,14 years old, I think I'd have accepted a cashout back then as I was on half a quid a week pocket money.
I do remember having £1100 when I was 14, 2 days and the bookies had 95% of it back.