I'm going to be using an RE Agent to look for some properties out-of-state, and I've been bombarded by quite a few people who have properties to show me.

a) What are some questions I could ask an RE Agent to verify if they are competent/experienced in the market? 

b) I know that agents profit if they sell stuff, so how do I figure out if someone is just trying to sell me something, or if it's a rental property that actually is cash-flow positive? 

c) What can I do to mitigate me buying a "lemon" rental property?

you will hire your own third party inspector to conduct an inspection which can lessen the possibility of buying a "lemon". Often times agents would hire an inspector they have been working with for a long time so it's best to do your research on the inspector. My last inspector was recommended by my agent but the inspector had over 200 positive reviews online. It also helps that you are present during inspection so you can ask lots of questions. Keep in mind that inspector will only do a visual inspection so if there are issues behind the walls they wouldn't be able to catch it.

Ask for referrals here, of agents in the specific markets where you are looking.