When you've sent them the second book, how long has it taken them to get back to you with comments.
I'm with a really good agent, but she's insanely busy and didn't read my first book for five months earlier this year. I then agreed a time to send her the rewrite after her comments, and nearly had a breakdown getting it to her for the deadline. She's now not going to read it for two months. I don't feel looked after at all.
Do I a) put up with this, it's normal, or b) make discreet enquiries with another agent or two.
FWIW, my last book got press coverage and was nominated for a prize but didn't sell that well, so I'm in the slightly dodgy middle ground.