I have been shopping around a good bit lately and one sales trick I have come across to disguise the true cost of the mattress is the box spring swap.  I wanted to get everyone's take on this.

They tell you their best price and then say that price can come down significantly if you choose another 'lower level' box spring.  This box spring apparently does not void the warranty in any way.  When asked the difference they will give very vague answers.

So my question is 2 parts:

Is this just a trick to hide the price and muddy the negotiations?

How much does the box spring really affect the mattress?

Thanks