Hi Britchap,
Most factory direct manufacturers and better sleep shops don’t have or need “fake sales” (see post #5 here) or negotiated prices (see post #6 here) to have great value and usually sell their mattresses at the best available price every day of the year … although of course it never hurts to ask “is that your best price”.
The most effective way to assess the “value” of a mattress is to compare it to other similar mattresses based on the parts of your personal value equation that are important to you rather than based on the percentage of a discount off a fake retail price that nobody ever pays anyway. I would treat stores that have ongoing “fake sales” as a warning sign and would generally avoid them (see the guidelines here).
Phoenix