I queried an agent I thought would be a great fit with me and my work at an agency. His assistant adored the MS but the agent did not and passed on it. Another agent at the same agency is an agent to one friend and one colleague of mine who both urged me to query the second agent regardless of the earlier rejection from the first agent. I thought this was greatly frowned upon.Yes, generally.
Yes, absolutely. The trouble you'll be in for submitting to the agency again (if they have a problem with that) will only be greater if they feel you've attempted to hide the fact.
I don't want cause trouble. And if I do query the second agent, should I mention the first agent in the query?