Then don't.
I think it makes sense to give back to clients and always have been of that opinion.
Good parenting taught me to give back to those that deserve a break now and then.
I won't.
It doesn't make sense to give back to clients if you will offend them.
It doesn't make sense to give back to clients if it will put you out of business.
It doesn't make sense to give back to clients who will not appreciate it.
Great parenting while growing up in extreme poverty taught me to give back to those that need and would most appreciate a break now and then.
So, if you are telling us that you have some objective reason to believe your client deserved a break, beyond simply them being a client, that is an entirely different position to take. If my clients are all rude, wealthy, selfish, and unappreciative, they would not get a dime under any circumstance. I should still probably take their money, because I am likely do more good with it than they otherwise would.
We all have a limited amount of money to give to others to help them out with a break. Them being a client of mine does not make them more deserving than the millions of child prostitutes I could try and help. Over 500,000,000 people live in extreme poverty on $1.90 or less a day, according to the World Bank.
So, when you state plainly "if you are in the service industry you need to give back to your clients now and then," I say, absolutely not.
Providing a service your client wants at a price they find fair is enough.
If your goal is to make the world a better place, most service providers are going to find a better way to do that outside of their client base.