Why do hotel rooms cost different prices on different sites?

I found alot of cheap hotel rooms but when i looked them up on different sites , it gave me different prices for the same type of room and the same dates? why is this ? is it possible to book tickets with a fake website?then be told that my reciept is invalid when arriving at the hotel? would be really greatful for any answers!

Hotels "sell" some rooms to various online booking sites, and these sites are then able to sell the rooms to you at whatever cost they want.

So -- let's say Hotel X has 20 rooms available for 1 night. They may sell 10 rooms to hotels.com. The hotel sells its 10 rooms for $100/night, and hotels.com will sell them for $95/night. You may find that the hotel will mark down their rates to $90 if they realize those rooms might not sell (and go empty).

But, be careful and closely read the TOTAL prices -- some sites don't show you the final cost (taxes/fees) until the very end of the booking process (so, the room looks cheap at the beginning, but ends up the same or more expensive than other sites when you actually pay).