This thread was interesting to me as well as someone who recently caught the domaining bug but with some experience with coupons.
There are literally a "million different possibilities . com" and people can run their usual formulas with how to get a price, revenue x years, CPC, exact match searches and throw in whatever else you use. But sometimes that will only take you so far. If somebody had some major sewing term .com you could run your formulas, come up with a number but if there is somebody that actually knows the topic/market on top of that, their insight would be a little better.
On top of that, since the $1500 was used and 4 years of revenue was $72,000 on some parked page. Ok, let's say they throw something up, something the search engines can grab and they start making 4 x that amount per month. So now that site is making $72,000 a year and if you use 4 x revenue, we're now looking at $288,000. Depending on how well you build it out, obviously that revenue can be very different. If you make it the authority site on printable coupons, a good quality site, $72,000 would be peanuts. Or you you throw up the typical domainer type landing site, it'll make more than it's making just parked.
I think the person who first bid $75,000 actually probably knows a lot about the possibilities and knew they would get a steal at that price.