My home is pre-wired with ethernet in every room, so their install shouldn't take longer than 10 minutes, just drop off a STB and add an IPTV login in my modem. I'm not paying $250 for that lol.
OTOH I can see a lot of older homes that have a mess of internal wiring and they spend all day trying to fix it. For those people, assuming are fishing and not stapling wires on the wall, $250 is a bargain. I paid $500 just in materials and tools to upgrade my place to CAT6.
If there is an issue with outside wiring, they could spend 7 hours or 2 days there.. they are fully liable so you don't have to worry about extra fees.
I guess what I'm saying is, they should decide the install charge case by case. If they spend all day on your internal wiring, full rate. If they come and go and everything works in 10 minutes, you shouldn't have to pay anything.