I think I would be really concerned about what would be involved in this shagging for someone to offer me a milion pounds. Would I definitely get it? Would I die and it be a sore consolation for my dd, inheriting lots of money?
That's an extremely good point, actually. People are mainly effectively thinking of lying back and letting him get on with it as though he were a normal, loving, consenting partner and you've said yes to his advances, even though you're a bit tired, albeit with the 'consent' bought/coerced rather than freely given.
However, considering how many men you hear of these days who automatically expect to be able to do all kinds of degrading and dangerous acts when they aren't paying a penny for it, what's the likelihood that somebody going to the lengths of paying a million for it is going to expect to really get 'his money's worth'? Has he chosen you in particular because he thinks you're absolutely beautiful or merely because he wants to be able to fulfil all of his nasty fantasies and desires with a 'human sex doll' - and by agreeing to it, you've self-selected yourself as that available object for his darkest lusts.
Some men deliberately seek out prostitutes, not because they can't get any with their wives/partners/casual hookups, but because they want to take it several levels further with somebody anonymous who means nothing to them and whom they don't really care if she gets hurt (or worse), don't really even consider to be properly human.
By paying you, they see it that they've bought you and, far from being an equal partner with equal rights, you have to shut up and let them treat you however they like; and if the prostitute has cost them £1m, and they like/fantasise about choking, gagging, multiple/extreme penetrations, forced poo-eating etc (sorry to be so graphic, but there are loads of surprisingly-popular disgusting kinks out there), they aren't going to think twice about trying to persuade you further, as you've already signed on the dotted line and they've paid for it.
To be blunt, if you'd paid £250 for an all-you-can-eat buffet, you would fill your boots shamelessly, defiantly and without holding back, and you most certainly wouldn't bother smiling nicely at the restaurant owner and ask pleadingly if they'd mind awfully if you had another plateful - in fact, you may even push yourself to have more than you actually wanted, considering the price; so if you've paid £1m for a woman....