I’d thought I’d add my 3 cents since I’ve done such low budget spots.
For me a typical $1000 (or less) spot consists of 4 hours of shooting (no crew other than me) and 4 to 6 hours of editing. That’s spelled out in the contract and that time includes revisions. They can certainly buy more shoot or edit time if they need You have to hold a very hard and firm line to that if it’s to be profitable for you.
Certainly clients may have someone supervise the project for them but that doesn’t change the terms of the contract. If a person attempts to takes such a supervisory position on the shoot I’d immediately ask the client if this is approved by them (and yes I’ve had to do that). If the client state’s that the person’s job then the “supervisor” has the right to muck things up.
For these low budget spots, the client pays 1/2 up front and 1/2 when editing BEGINS (not ends). This is another firm position you’d need to take in order to make these kinds of jobs profitable to you. I do send the client a window dub of the shoot on DVD so they can make any assessment of the material (know what they have to work with for the edit).
If after the terms (shot and edit time) have been met and the project isn’t complete, the client has to decide if they want to pay for additional time.