NEW YORK ( MainStreet) — It fries you. You are sipping a wine at the hotel's free social hour and you overhear that guy over there, "I love this hotel, especially at $139 per night."

You paid $175 and you thought it was a deal.

How did this happen?

Face facts: in the Internet era, hotel pricing has become a crazy quilt. It used to be that there was one price and that was that. Now, pricing is dynamic, as hotels stumble into what's called revenue management, which amounts to attempting to squeeze the best price out of every booking, even if that means the price changes every five minutes.

Another fact: hotels typically reserve their best pricing for what they call "opaque" marketplaces, such as Priceline's Name Your Own Price program, where you bid blind, not knowing what hotel you are bidding on, but knowing the neighborhood and the star rating.

The reason: a growing annoyance for many hotels is a sharp increase in the number of guests playing what could be called room rate arbitrage. It works like this. You book a room for the night of February 14 in San Francisco, and you make it a fully refundable booking. Then you keep checking for lower rates. If you find one, book it and cancel the first reservation. Then the game begins anew.

That, incidentally, is the insider's tip for always getting the best rates. The downside: playing rate arbitrage takes work, constant monitoring.

Hoteliers will not disclose how much of this arbitrage occurs but, because the Priceline Name Your Own Price deals (and similar from competitors) are opaque, they don't figure into this arbitrage because they don't show up in Web searches.

Remember "opacity," however, because that is the word that, eventually, will unlock yet more savings.

The blunt reality: hotel pricing is guided by what the industry calls "parity," said marketer Edward Nevraumont, a onetime Expedia vice president. What "parity" means is that when a big online travel agency (OTA) - like Expedia, Hotels.com, etc. - agrees to handle a hotel, it usually insists on "parity," which means no other site can offer the same room on the same night at a lower price and neither can the hotel itself.

That means prices, really, are pretty much the same in an apples to apples comparison.

But not always. Drew Patterson, CEO of hotel price search site Room77, said that his site uncovers significant differences in prices at hotels 60% of the time and that those differences can average around $40 per day.

How? Often the price differences revolve around special discounts - for AAA membership, for instance. Often, too, hotels on their own sites offer special deals - free breakfast or free WiFi, for instance -- and Room77 makes a point to patrol some 100,000 hotel sites.