Lay down some ground rules in writing before you start. Seriously, this group of people are a different breed. Every one of those units is a person and a lot of those people have some degree of animosity against the HOA board. This is to keep you from becoming a victim in the never ending little battles amongst different owners and the HOA itself.
No work stoppages by homeowners. Somebody might try to play passive aggressive games by intentionally leaving windows open, etc.
All communications through one person only, do not allow the entire HOA Board to become involved in any way at all if your main contact is the property management guy only. He is the main and only contact and it stays that way
Set expectations before starting and in writing. Note EVERY defect you find before starting and every little thing that will not come clean. It may take a few hours but you'll be covered that way. Smeared stain/sealers on siding, heavy oxidation, etc.
Do NOT allow anybody to follow you around while working. There's a good chance one of them will try. set the pace of the job and put in writing the order you will be going in.
I will never give an HOA a substantial discount. Small yes, but not sizable due to potential headaches. Just be careful brother, these people can be an odd group. Some run smoothly, others are a mess of politics, personal vendettas and squabbles amongst each other.