For some, time is money.
I could literally spend a month of Sundays driving around to every hamfest in creation looking for a somewhat rare but needed piece of equipment...or I could pay $50 more than the thing is worth through eBay and spend all those Sundays doing billable work.
The difference would be made back in 1/2 an hour, by the way.
Obviously, this is a ludicrous approach to take when contemplating the purchase of something as common as, say, a TS-820S or 440 but rest assured if I want that SX-88 or 75S3-C badly enough, I will get it.