Hi Paul,
Yes we do it. There is money in everything if marketed correctly and if you do a good job.
You need the right insurance, and special vacuum cleaners. I have some spare for sale going cheap.
You will be up on competitive market though. The larger firms have the contract sown up but the cleaning is not fantastic. This is where you can win. On average you will go back on regularity on a 6 months basis or 12 months.
You need the vacuum for the inside of the PC. To clean the motherboards and fans.
Let me know and I will let you have an email address and let you have as much info as you need.
Dave