Hi Sheepcounter,
You can read a little more on flipping and rotating a mattress in post #2 here. Your mattress is one sided so you can only rotate it.
I would treat these types of fake sales that never end (and only change in details) … as a warning sign. They are typical of the types of stores I would tend to avoid (see the shopping guidelines here). There is more about fake sales in post #5 here and about negotiating in post #6 here. Most of the more common questions that people have when they are shopping for a new mattress are also answered in the mattress shopping tutorial.
The price you paid for your mattress is actually in a fairly low budget range. While the quality of the materials is a big part of the cost of a mattress … most major brands retail for more than their smaller independent competitors that often use the same or better quality materials in lower budget ranges (see post #12 here).
You can see the specifics of my mattress in post #4 here.
Phoenix