Are there limitations on replaceing a crown less than five years - where the dentist would have to replace the crown free due his his poor work?

That is dependent on the dentist. Some have warranties, others don't. If you have dental coverage, most insurance companies (at least here in Canada) won't cover anything unless it's been over 5 yrs.

What makes you think the dentist did poor dental work?

I had a dentist that was going to crown a tooth of mine but I ended up going to another dentist because I didn't like the 1 I was going to.I am so glad I did the other dentist told me that if I had that tooth crowned it would not have lasted because I am losing bone structure in my gums and it wouldn't have lasted and been a waste of money.