@Mor - If a dog has been fed a good diet and hasn't got any genetic problems (like the ones that often come from inbreeding) then there shouldn't be many incidents of the sniffles or other small illnesses.
And if a person can't afford to take their dog to the vet if they need it, then they can't afford a dog. It's just not fair to keep an animal if you aren't going to be able to look after it when it's sick.
That said, giving your dog milk thistle capsules when it's recovering from something, or when the vet thinks it's a good idea isn't going to hurt your dog. This isn't some quack remedy, vets will prescribe it and you can also get it in pet stores as a supplement.