Getting back to what (I think) was the original question, I think the answer is to go by instinct.
Minor 'slip-ups' in maintenance are not necessarily serious (though they may be), but the critical point is how much attention you (the customer) is getting from the club or school (the supplier). Don't settle for second best. It's your hard earned money you're spending and you should make sure you give it to someone who takes you seriously as a fellow pilot. You can be sure that if they're not bothered to respond to your concerns over little things they'll also be unhelpful over things which are big (to you at leasr).
i've learned from experience that there are some wonderful people in aviation, and I'll go a long way to fly with, and learn from, them. And there are others who are fine in their way, but who I do not want to give my hard-earned cash.
So follow your instincts and move, you're sure to do better elsewhere.