My book was sent on time but the post took 7 days. This is hardly my fault. I have proof of posting and the package should have stated when posted. Can I ask for the rating to be changed?

It is unfair if people not only stick too rigidly to the 7 day deadline thing, but also don't check the postmark to see when the book was sent.  Unfortunately, there's nothing you can do to officially query the rating you've been given.  The best thing to do is to send a friendly little email to the other swapper, apologising for the fact the book was slightly late and explaining that you sent it within the guideline time so that it's not really fair to hold you to account for RM's slow delivery.  You never know, they may well be persuaded to upgrade your rating, but if not then I'm afraid you just have to accept it as one of those things.  The 4* rating will soon move down your feedback list, and most swappers will not be put off swapping with you on the basis of one lost star. 

One way of letting the swapper know you have posted the book in time so they know its RM's fault for delay is to make sure you click the "I have posted this book" the day you post then the swapper knows  its on its way.

Tonibat, having cross-checked the feedback left by you both on this swap, I see that you received your book the day after the swap was agreed, but marked the other swapper down for the fact you felt the spine was a bit more than "slightly" creased.  It may well be that the other swapper felt this was unfair, as measuring book damage (and especially spine creasing) is incredibly subjective,  and so they are now retaliating in kind.  As a result, you probably won't get too far with them by sending an apologetic email, so my advice would be to just draw a line under it and move on.