Cost to Renovate bathroom
This part of Don's answer follows my thoughts exactly:
"You want to deal with a professional person that is selling you a bath that was not working as a cashier a few months ago."
Do you go to the gracery store and ask for someone to cook your steak? Of course not. So why would you go to a building supply store and ask for someone to remodel your bathroom? Rarely will you see a legitimate contractor take jobs from a retailer. Why? Because they don't pay much. Speed is the most important thing to them, along with getting it done cheap so they can maximize profit. About 10 years ago I worked on a few contracted structures (sheds, garages, etc.) from Home Depot. They contracted to another company who then contracted people to build them. At that time they paid a flat $250 for a contractor to pick up the supplies, build the structure on site, paint it, and use their own tools. By the time the cost of a helper, fuel, tools, etc. was factored in there was nothing left for the contractor. Anyway, the point I'm making is that the guy who will eventually show up to do the work will be so far down the line that everyone else has already taken the profits (Home Depot, ReBath, possibly someone else, and finally the guy working) that he probably isn't going to care what kind of job he does for you, quality or not. He likely won't have much experience due to a high turnover rate and any experience he does have will probably be limited to his teachings at that job. He probably can't answer any building code questions or identify other hazards once things are taken apart and he certainly won't do anything he doesn't have to while it is apart.
Another problem I've heard of repeatedly is that if (when) there is a problem there is always someone else you need to speak to. You might have to talk to 4 or 5 different people before you can even get to someone that can address the problem. Now multiply that due to having (at least) two separate companies involoved. "You need to call ReBath." "No, you need to call Home Depot."
You hire a general contractor for a reason. We learn, understand, and keep up on building codes. We are the one point of contact for all questions and issues on a project. There is no manager in some other store, state, etc. to call. You contract a GC and deal directly with that GC, or a site supervisor in some cases. There isn't a huge chain of command to get through to reach the main decision maker for the business. In a bathroom remodel you need someone who can do the plumbing, repair and/or move any electrical, install tile/flooring, drywall and paint, trim carpentry, and someone to coordinate all of that. Sometimes you can find a qualified contractor to do all of those things and sometimes he will sub-contract out certain components (especially due to licensing laws) but you will always have that one definitive person to go to for any questions or issues. A salesman in a store doesn't visit your home throughout the project to check on the status. Even if he did, he likely wouldn't now what he is looking at. The same goes for a retail manager.
Hire someone who specializes in taking care of your home. Hire based on reputation & knowledge/experience. You are right that not every customer can be happy so an occassional bad review can be found on just about any business. Read the reviews, not the grades (they are always biased). Look to see if the contractor attempted to rectify the problem, not ignore it. Lastly, unless you want cheap, sloppy work and a whole heap of other troubles, don't hire based on a low price.