In my experience vendors will stop trying to push you around if you show them the ISG and that what they are trying to push on you isn't there. But don't treat vendors like shit unless needed. Part of their job is to try and get stores to set up displays for new products/specials, and I've seen ETLs/STL treat some of the best vendors I had like complete shit because that's how they interacted with everybody. Just be firm and fair