This may not always be the case, but sometimes you have to keep an open mind: Sometimes, the ads are old. If they put the age of the bunnies as 2 weeks, and several weeks go by before you see and reply to the ad, they won't be 2 weeks anymore. Many advertise bunnies at that age so that they can have them ready for new homes as soon as they are weaned, instead of racing around to get them homes at the last minute.
This is why many people only buy from reputable breeders. Because, they are just that, reputable. You always take a chance when buying from an ad, or someone you don't know (know about).
This is why many people only buy from reputable breeders. Because, they are just that, reputable. You always take a chance when buying from an ad, or someone you don't know (know about).