Jim,
Around here there are not a lot of used Glocks on the market. The ones that are available are usually police trade-ins. When the depts change calibers or size they sell off the old guns. They usually go for about $350-$375. So the price doesn't sound out of line. If it is a police trade-in it was probably fired about 200 rounds a year. You'll never wear it out, and the 19 is my favorite size in the Glock.
Stay Safe,
Savage