too hard or too soft?

I personally prefer a firm mattress, so earlier this week, when I went shopping for a new bed for my guest bedroom I decided on a firm mattress.  I bought the mattress at Mattress Warehouse and was very pleased to discover that they provided free delivery and set up and would even haul away my old mattress.  I had checked at a different furniture store recently and was told that they charged a $100 delivery fee, no matter what you bought.  No surprise that I opted for free delivery.  But what I really like, although I hope not to have to take advantage of it, is the fact that if I'm not happy with the mattress they will swap it for an equivalent model.  The salesman specifically mentioned that if the mattress is too firm I could exchange it for the softer version of the same model.  My first guest to try out the new mattress will be visiting this weekend and another couple will be here at the end of the month.  I'll be interested to get their reactions.  And no, I didn't deliberately get the firm version so guests won't over stay their welcome.  How could you think such a thing?