Excellent answer Chris.
I take exactly the same approach (to domestic work anyway) and have been turned down on a few occasions recently. It's very easy to offer to do it for less, but there are certain prices that I just wouldn't bother turning up for. Since my leaflet campaign started, I've had a few 'quote requests' from other cc's (you can generally spot them a mile off) and I can never understand why they do it. If they're that confident of their own service and ability, why should they worry about me? I certainly don't give a **** about them and what they charge.
I always go through the full routine from pre-vac through to final carpet groom, and if anyone thinks I'm going to do all that for about £10 an hour, they must be joking. After all, I've got the outlay on an Eclipse and Super Pad Charly to recover.

If these 'customers' want to pay about £50 for their whole house to be cleaned, then fine. I'll just wait for the call when they tell me "I had this cleaner who did my whole house in three quarters of an hour, and it looks...."
I do, however, try to look at other companies' charges where commercial jobs are concerned, as cost is an extremely important factor to Facilities Managers with generally tight budgets.