You don’t have to shoot them to loot them as their wrecks are blue due to their criminal flag but of course it can still be fun to shoot them for the sake of it and maybe to try prevent them to succeed.
You can also grab the loot of the victim if you so desire. You can justify it by roleplaying that you do this to prevent the gankers from scooping the loot. 
Speaking of which you might also kill off the loot scooper ganker alts if their ship is something you can succeed in killing, which is also some potential pew pew opportunity.
Some related links…
Stealing from gankers (both the loot from their victims and their own) plus some pew pew and other fun stuff.
As you mentioned selling corpses.
Some ganker scouts and loot scoopers can be juicy if they ganked a juicy target beforehand.
https://support.eveonline.com/hc/en-us/sections/201141682-Crimewatch
Some basic useful (official) info, though best to learn these in-depth by reading further other sources and observing and practicing their use in-game (a good place is around Jita 4-4).
Good luck and have fun! o/