I have worked with many other syndicates over the years in various fashions and now I take on partners as well.
Biggest problem I have run into when working with certain syndicates is when they start using your "smaller" accounts to manipulate lines so they can pound the other side with their bigger accounts. Do not be fooled by the nice guy image a lot of these guys throw out there.
Most guys are honest and understanding on many levels but some of these guys that are out there will go to any length to increase their EV at your expense. And then when they say they are sorry and will stop doing it they go right back to it.
This is not the case with everyone but this is the most common problem I would imagine. I would be happy to answer any other questions you might have