Instead of a single number, should the "score/max_score" be listed? A 7-out-of-7 (7/7) is a 100% top score for great service, at the 7-level, and "7/7" gives you both pieces of info. A 10/10, is great 100% service with some extras. A 7/10 is still good 70% (a passing grade), but not as good as a 7/7 100%. Or maybe you want more services (/10) and will accept good, rather then great, service (7/).  score/max_score give you that info to chose.

Instead of showing both numbers X/N, just show the per cent as the score?  Now you don't know which factor is more important. Is it 85% for lack of a service (6/7 = 85%) or for a less than "10" performance (8.5/10)?  

What if we just switched to -1 0 +1