The vet laughed and gave us a prescription to get rid of them.
Do you think that's because the dog's problem is not too serious?
Yes, and I'm not paying her for my pet's care most of the time
It's good to take your pets to the vet if they have any problems, even just fleas, because the vet can give them the medication they need.  Your vet should not be laughing at any condition that requires a prescription, though, and you shouldn't be taking advantage of her for free medical care.
Well, my vet is not an average one, but I don't care because I love getting something for nothing.
You should be paying the vet for your dog's medical care because taking advantage of your vet for free services will weaken your resolve when things get really financially difficult for you one day.