Where do you buy your wormers?

[Lippitt]

Wormers for dogs. I've always got mine from the vet but looking online it seems I can get them a lot cheaper from buying online. My question is as there are so many sites to choose from, how do I know they are genuine sites selling genuine products? Does anybody have any recommendations? If you tell me they are all dodgy I will of course continue to buy from the vet, but if I can save some money without compromising safety/effectiveness I would like to - more money for treats and toys!

[Lippitt]

Thanks very much for the help! I think I'll give it a try.