Well, I'm not really the one to judge good or bad. Revenge spells are pretty complicated. Sometimes, if the spell does work, you may think you got the upper hand - the person might get whats coming to them and that can happen in many ways - some of those ways can be really bad. that can lead to guilt on your end.
More importantly, Hexes, curses, revenge spells do break the harm none rule. its sending out negative energies (created by your anger/hurt/etc towards them) and whatever energies you send out will come back to you. If you're sending bad, you will get bad. Karma works in that way.
All in all, if you cast a revenge spell you might get the result you want or revenge but it could easily backfire and leave you in a bad place.
i messed around with cursing for a while, i was really angry at different people who hurt me in my life and I thought that was the best way to get back at them. It ended badly, on both ends. i swore I wouldn't do it again, because it was starting to really mess up my life.
what I suggust you do is what I did. Take the issue to a deity (Often use The Morrigan for this, Goddess of justice) and let fate fix the issue as it sees right. Karma will run its coarse and those who did bad will get bad back.
Give the issue up to fate and do some cleansing and releasing of the negative emotions you feel, work on building yourself stronger and being able to move on.
Sometimes the best revenge is proving that you can be the bigger person.
Well, if they were doing or saying bad things to you to begin with, this may be a cut and dry case of, "Karma is a B*tch", excuse my french, but my meaning is that Karma may have just handled the situation for you. Also, showing people up for not believe you, where magick is concerned, is somewhat childish. Try some protection spells out and see if that maybe blocks their negativity.