There are quite a few limits in place to prevent minor abuse of the reputation system. Obviously there cannot be a flawless system, but these limits try to curb any intentional abuse. You must have 25 posts and 10 reputation points in order for your reputation to count on other people. Until you meet those requirements, your reputation will show up as grey dots (see below). Everybody is limited to giving out 10 reputations per day; you cannot give the same person reputation until you have given reputation to 2 other people. This prevents friends from giving 10 reputations to the same person every day.