Probably the best advice I can give you is to ignore the salesman, and go find somebody in the service department that looks like they know what they are doing, and ask them. When somebody asks me, I give them a "yes", "no", or "maybe" answer. And 90+% of the time, "maybe" means "no".
If there's a question about how much your tow vehicle will tow, look in your owner's manual. It will tell you in black and white how much you can tow, and under what conditions. 10,000 pound tow capacity does not mean you can tow a 10,000 pound 5th wheel with your half ton pickup. It means that, with the proper engine, transmission, rear axle ratio, suspension, brakes, and other optional equipment, the truck can tow up to that amount, before subtracting the weight of passengers, fuel, food, even the extra-heavy-duty battery you had put in the truck last fall. Some tow ratings even state a maximum frontal area for the trailer you are towing, usually something like 60 square feet.
So, after you deduct all that stuff, you will probably end up with a real world tow rating of about 8000 pounds or so.
Yes, that's my trailer in my avatar, and no, I don't tow it with that little bitty car sitting in front of it...