Hi Bunsen, that`s pants when scummy people do that! people who cannot afford wheel arch trims, should stick to riding scooters, and roll up their jeans in to their socks, if you know what I mean! They are really easy to fit, just line up the new trims to the studs, and the round disc`s, flush to the body work, and then push on the arch anti-clockwise. real easy, certainly do not need to pay out 70 squid!!
Just take your time, it`s a great learning curve. The trims come with a bag of fittings, but as you wont need them, they are great to have as spare.
If you dont feel confident doing them, get somebody like your dad to do them, I always find dad`s a great at certain things like this

If not; all is required a mate, or even a local garage bung them 5 quid, they will do it!
But to be honest, best to do it yourself, it`s as easy as pie, once you have done it once!
Enjoy that MINI and dont let some plonker ruine your MINI experience!!