MGR stores are franchises, I don't know if that means the store has more or less pricing discretion than Guitar Center and the like. Shipping always seems high. I would need to check anything out first hand before buying. The return policy at Guitar Center is tough to beat. OTOH the MGR nearest me usually has something cool, also a few bizarre things I've never imagined which are sometimes cool. Prices range from slightly higher than I've seen elsewhere to a good bit lower, not counting the prices on things I've never seen anywhere else. It's worth keeping an eye on the one closest to you, sometimes worth the trip for me even if it's an hour +. Just traded a bunch of cool stuff I hardly used for a couple of cool things I'll probably hardly use.
Never tried negotiating, I'm not going to drive up there if the price isn't acceptable on whatever has me making the trip. Every place that takes trades always asks "How much are you looking to get" to which I always reply "As much as I possibly can."