Kevin…in my opinion, it's not a bad habit to get into…it's not a bad thing to work with horses you want to work with...here's why I say this…
1. Owner's don't pay for damage done to you or your facility by their horse once you've accepted the horse for training.
2. It takes more time, effort and risk to re-train/undo/"fix" a problem horse than it does one that needs tuning, finishing or to start one from scratch.
3. Working with the same type of problem horses won't make you a better trainer…working with better horses will. Fixing problems isn't the same as teaching a horse how to give it's personal best. Better horses means better money. And you can't accept a good horse if your barn is full of problem ones because you don't turn down horses.
Re: Owners - they'll tell you what THEY have a problem with and it will seldom be what the problem really is…if they knew what the problem was and how to handle it, there wouldn't be a need to come to you in the first place. Owners do what I call '"creative omission" - they'll tell you enough so that you'll understand the horse needs work, but not enough to scare you off…especially if you are priced right and have an opening!
What you might think about doing is evaluate potential horses, for a fee, upfront, then determine whether or not you'll take them in for training and what it'll cost the owner if you do. That way you'll get to see how the horse behaves when he's "at home", what "at home" consists of and have the owner handy which saves on phone tag later. IOW, do your "first hour, first ride" there - for a fee - in front of the owner.
Just my .02 cents worth on the subject.