After being rejected by one agent in an agency, is it a good idea to send a query for the same book to another agent in the same agency?
It is frowned upon, read the submission guidelines they should tell you if they allow it.
After being rejected by one agent in an agency, is it a good idea to send a query for the same book to another agent in the same agency?
Very, very few agencies have more than one agent for a particular type of book, and when a query comes in, that agent is the one who reads it, no matter who the query was addressed to.
I strongly disagree. There are some genres that most agents represent, if you have a popular genre then most agents at the same agency will cover it. One might like it, one might reject it.
There's no absolute wrong or right here: so much depends on the agency concerned. I think the important thing is to read the various agencies' guidelines, and act accordingly.