I can't believe how your client wants to complicate things, how much you try to help, and how all comments here beat around the bush with savant solutions ...
What if reality will show just a few testimonials with typos, bad grammar and poor ratings?
You can simplify things by inviting visitors to offer their opinions asking them to type the number of stars by themselves.
1 star *
2 stars **
3 stars ***
4 stars ****
5 stars *****
Remember: less is more…