yeah, Predators are "hunters", and who the hell knows what exact standard they consider fair for hunting. Our standards are hard to define. baiting, sniping, flashlights, etc. versus fishing.. nets, etc..
sniping from their space ship, is apparently not fair. They have the tech. Giant bombs is not fair. (but ok to use to prevent their tech/bodys being taken) and even that its not clear which it is. is the self destruction to prevent themselves from being taken as a trophy? or just to keep the tech out of others hands? the later movies, showing predators honoring humans, would suggest its more about keeping the tech out of human hands.
Avp did show them change weapons when dealing with xenomorphs, showing they do handicap themselves to their target.