Tell me, how should a student pilot with low hours judge an instructor ? When does he know he has to change or he can get a better one ?
It's difficult. What's been suggested already is good - try an hour with someone else, and see how you get on. But here are a few pointers...
1) Do you get briefings before new exercises? Recently I talked to someone who'd done quite a lot of the course, and almost never had a single briefing. You should be getting some, even if not before every lesson.
2) Does your instructor appear to care more about whether the flying conditions are right for you, than whether he's making any money. If he/she wants to fly no matter what the conditions, be careful. It may be good practice for you to learn to fly in marginal conditions, but it may not.
3) Is he/she avaialble when you want to ask questions. The person I talked of in Point 1 said he asked a couple of simple questions...and the instructor turned round and charged him £50 for ground school!!!!! If you want a ground school course, fine, but charging for a couple of questions, NO!!!!!
4) Do you get on with him/her, and do you appear to be making progress? Students often tend to blame themselves if they're not making progress, but another instructor may be better for you, even if there's nothing wrong per se with the one you've got. Worth trying someone else to see.
5) If you're worried about what your instructor will think if you fly with someone else, tell them the truth, that you just want to get another point of view. And if they get upset about it....well, I'd be wary of someone like that. It's YOUR money and YOUR flying and YOUR choice.
Hope that helps a little.