Just last week, I saw a dive shop refuse to fill tanks, that were hydro'd direct, and then they proceeded to call another local shop and tell them not to fill them. Whoever it was, was from out of town. I would rather deal with the hydro facility directly too. Anyway they did not appreciate getting bypassed on the overpriced fees I guess. In any event, I have had my tanks hydro'd twice, at 2 different shops, in two states, and had no problem.
There are certainly shops I would not leave my tanks at for hydro, or anything else. Find a reputable shop that is professional, friendly and hopefully develop a relationship, etc. If they are disorganized, have an attitude, overcharge you, keep prepaid orders and never deliver product, charge for classes they don't deliver on, etc... then you are in the wrong shop, don't try and argue the point, just go elsewhere. Most shops I have seen are professional, friendly and competent. They only way to root out the bad ones is to not give them your money. You should be confident that most shops will treat you right and earn your business.