Be ABSOLUTELY straight honest with VA.
Link to 38 CFR 4.16
If you want to deal with VA and the scrutiny of wether what you do is marginal or gainful, that is up to you. VA will be notified and they will decide. Here is a quote from Cruiser on this:
"When VA is notified of earned income by an IU recipient they do the necessary development to determine the nature of the employment. If it is determined to be marginal employment, then the question is whether or not this is all the veteran is capable of doing. In almost every case the answer is "Yes;" however, this should not be considered to be automatic."
Quote from another post:
Post is a process in work...If an IU Vet goofs around here and there and earns a few extra bucks, fine. There is a difference in sporadically doing things to make a little money and maintaining substantially gainful employment. Marginal is not substantially. Just be up front with VA or you could end up butt hurt.
"Veterans who are in receipt of Individual Unemployability benefits may work as long as it is not considered substantially gainful employment. The employment must be considered marginal employment."
"Marginal employment shall not be considered substantially gainful employment. For purposes of this section, marginal employment generally shall be deemed to exist when a veteran's earned annual income does not exceed the amount established by the U.S. Department of Commerce, Bureau of the Census, as the poverty threshold (see link below) for one person."
Link to "Poverty Threshold" info.
There. That's it. Pretty freakin' clear cut in VA speak.