Flea shampoos don’t keep fleas off dogs, they just kill the fleas currently on the dog. Any type of shampoo will get a dog clean and kill fleas, so if you don’t have money for specialty shampoos, you can use standard human products.
Bathe only as often as necessary. Frequent bathing will dry out a dogs coat and cause skin problems.
If your dog has sensitive skin, use hypo allergenic or calming shampoos like oatmeal. If your dog has picked up some dirt but isn’t smelly, try wetting a towel and damp toweling the dog. It’ll remove most of the dirt without stripping the oils from his coat.
If you dog rolls on the floor or in the dirt after their bath, try an unscented shampoo. The smell of perfumes in shampoos is unpleasant to many dogs.