DON'T buy from an add that mentions "Easter", unless it's saying that "Easter bunnies" are not available.
DON'T buy mixed breeds from a backyard breeder that has no idea what they're doing.
DO buy from someone that is a member of the ARBA and his/her respected breeds' clubs (Holland Lops have many clubs about them. The breeder doesn't have to be a member of all of them!).
DO buy from a breeder that can answer your many questions. What the breeder says will not only line up with what the internet or what books say, but it should be logical and obviously researched or learned from experience.
DO ask about the breeder's credentials. How long have they been breeding, what breed do they raise, where your rabbit comes from, ect.
DO, DO, DO ask questions, questions, questions!!!!
If you don't care about breed, and don't need a purebred rabbit, consider buying from a shelter or rescue. Mixed breed rabbits do make good pets, just as any purebred can, but it's not worth buying a random "dwarf bunny", or "lop-eared rabbit", to support bad breeding practices.
Purebred, good-quality, pedigreed rabbits will cost more then a backyard breeder or pet store. But know that you are supporting their hobby and investing in someone that raises rabbits for the right reasons.
From reputable breeders, the rabbits will be healthier, have more personality and better temperaments, have lots of time spent with them and know what's expected of them as a show rabbit, breeding rabbit or pet. You'd pay more for a rabbit that will be a definite weight as maturity, that will look a certain way, whose personality is pleasing and cute, rather than paying little money for a rabbit with a skittish and boring personality, with no sure weight limit, and no way to tell what it will look like at maturity, wouldn't you?!