I just recently decided to quit the "every once in a while" and go to every other week - and I will save quite a bit.
1) If you're using a service, they should have a printed copy of what you should expect. You can subtract some things (I like to do my own linens), but usually it will cost more if you ask them to do something extra (ie: clean out the refrigerator).
2) Unfortunately, both my mama & I tidy up before they come! For one, if you are paying by the hour, it will take them less time. In my case, it keeps me more apt to clean.
3) I'm going every other week starting January. Before that, I had them about 4 times a year.
4) I now use Molly Maids - $62.00 every other week, less if it's once a week, more if it's less often. The Maids (who I used to use) charge $100/hour - and their maids only get paid minimum wage! I found that outrageous!
5) My mama used to use a cleaning lady who she heard about. I would ONLY go word of mouth, if I wasn't using a (bonded) agency!)
6) Yes, I'm there. I tell them what's most important to me, and then go into the one room I don't ask them to do and play on the computer!
7) If you're going to interview a person, rather than use a team, be sure to ask them if they're comfortable with what you'd like them to do. Have a list prepared. Ask them for references WITH phone numbers, and if they'd mind if you ran a background check. F YI, I'd have no problem hiring someone who has been arrested, as long as it wasn't for theft. Asking (note that I didn't say "demand") about a background check will have the person who had a DUI when they were 19 admit it up front - usually. Also, ask them how long they think it would take to do your house, and take them for a tour.
Good luck!!