the price can always be adjusted based on on or off season, amount of colors to be used. A job like this can be done in 2 days and much quicker with a helper. I charge a bit more than others just because its quality work done professionally. Theres others that charge more than this just because they can on the on season and most people dont get a 2nd bid...
I was a painting contractor for many years and never asked for a deposit upfront. A good contractor should have great credit with his suppliers and an even better contract if the deal should go south before the job is done. Get to know your customer and explain how each paint covers so they understand fully before you have to apply 3 or 4 coats. If you didn't bid your job right and the client has already signed the contract then that is on you not the client. Yes I haven had to eat the difference but the client was happy and a return customer for years so I made up for it.