Any sticker/advertised price is what's termed in law as an "invitation to treat". It's not an "offer" in the contractual sense. So until you agree to pay a price it's really just a number and can go down or up.

Most stores will have some sort of discretionary Manager's discount and I'll bet they hardly ever use it and really really want to! I bought a load of scalextric the other day in Model Zone in Kingston [for my spoilt nephews, not me]. Tag price £250, I paid £200 and the salesman was gutted [I asked for the manager] as he reckoned his own staff discount didn't come to that

The only thing I draw the line on is when they try and offer you warranties, finance or store cards in order to get the discount.

Cash is key as said above, if someone comes into me looking at cars and says "I've got £XXX here and I'm out today to buy a car whether it's from you or someone else" they won't be walking away.