3rd Party Sales Reps

Has anyone here have any experience working with, for or managing 3rd party sales reps/agencies?

Its a very common thing in the industry I have to work with reps who carry multiple lines of product. I manage an agency in one of my areas, it is all very new for me and its meant handing off an area I have spent the last year developing to a bunch of people not directly employed by me but rather working on a commission only basis at the same time as selling several other lines not related to me.

The positives to it are, they tend to have good relationships already with my clients due to dealing with them on other lines so it can make opening doors easier and faster and they are boots on the ground so I can travel less. The negatives I see right now, I dont know yet if they are going to attack it with the same fervency as I did because of everything else they do/sell.

Anyone got any experience in working like this? Be interested to hear both sides, if you worked at a rep agency what did you look for from your vendors?

This may be a little niche considering most here are in tech but its worth an ask.