Etiquette in dealing with contractors

[Gustavus Adolphus]

I made a contractor very upset by not accepting his bid and am trying to figure out if I broke some important etiquette rules of dealing with contractors.

The story is this: I got two estimates from painting contractors for exterior painting of a large house. Company A's bid was for $9500. Company B's was $8800. I asked Company B to come down to $8000, which they agreed to do. I then told Company A that Company B had lowered its price to $8000, and asked if they would match it. Company A agreed to do so. I had a slightly better feeling about Company A, and since the price after negotiations was the same, I ended up going with them.

I wrote to Company B politely to say I really appreciated the time they had taken to give me the estimate, but had decided to go with another option. I got a nasty message back saying I was untrustworthy and of low morals.

I got the sense that Company B didn't like that I backed out after they had agreed to come down in price. I worry that they thought that, when I asked them to lower the price, I was implying that I would accept their bid as long as they agreed to the new price, rather than going and asking their competitor to match the new, lower price before making a final decision.

Company B also spent a long time discussing details of the job over email with me over the course of a week or so. I think part of the offense they took may also have been from the fact that they had invested a fair bit of time in working with me, and I had then turned around and not hired them after seeming to be very interested (which I genuinely was -- but I also wanted to make sure I was getting the very best balance between price and quality that I could).

I don't have a lot of experience dealing with contractors, so I'm honestly wondering if I committed a big faux pas, or if Company B is just unprofessional. When I ask a contractor to lower their price and they agree, is it nasty of me not to end up working with them?

Just looking for some perspective on the issue.  In the future, I want to avoid burning bridges with contractors who give me estimates, since even if I don't want to work with them on a particular job, I may be interested in hiring them for different work at a later time.