If it's a dual lnb with a multiswitch exposed on the outside, make sure they put in a drip loop, this should cost nothing to you extra, it's supposed to be part of the install. If they drill holes, make sure they have the wall grommets/sealant to keep them from leaking in drafts/water.
If it is a dual lnb, you might want to install yourself a weather-proof box near where the dish and switch will go so they can use that as the place to put the switch and grounding block (make sure there is a grounding block put in btw).
If you are getting HD, then you will have a 3lnb dish, in which case you can probably ignore the drip loop and weather-proof box advice, as the switch is built-in(unless you want the grounding block weather protected).
Make sure and run a signal meter test (on the receiver) before you sign anything after install, if the signals aren't in the mid-to high 90s (assuming you have a perfect line of sight for the dish), then don't let him leave until they are.
And based on advice seen on this forum: If the guy asks to borrow a ladder and/or doesn't have a ladder, ask him to leave, and get a new installer.