Okay one way that you can is removing both balls from each barbell and soaking them in rubbing alcohol for about 4-5hrs, remove from rubbing alcohol to dry and then putting them back together. The rubbing alcohol will kill any germs or bacteria left in them. I learned this in Dental Assisting school. Since you most likely do not own an Autoclave (a machine that can sanitize using water at a dangerous hot level, I used to clean mine a few times while in school and work) rubbing alcohol is the next best thing either to clean them or if your were to resell them. I hope this helps :)
Lol I figured as much. You wanna make sure that they are really clean before you give them to someone else. You don't wanna pass along something that may be contagious. Not that I'm saying you have something, I'm just saying in general.