To me, the ASHI Code of Ethics is VERY clear.
1A) "Inspectors shall not inspect properties for compensation in which they have, or expect to have, a financial interest."

The way I see it, you are going to have, AND do EXPECT to have a financial interest. You plan on getting paid to do construction work, AND you plan on sharing the profits from the sale.

IF you get paid for the inspection, AND get paid for the rehab work, you will probably be ahead of the potential profit line, unless the property is purchased at a steal.

You need to look at who is bringing what to the table.

You have the inspection skill. Can the investor get the same job for the same amount of money from someone else? Probably. Cost involved - probably $250 - 500.

Running the job. Assuming you have the proper licenses (could be a big problem if you don't) and skills AND experience (bigger problem if you don't). Can he get this same service somewhere else at less cost? Maybe yes, maybe no. If there are a lot of tasks that you have to hire out, then your worth (to the investor) is less. If you can't get the job done in a timely manner, your worth is less. Cost unknown.

The bottom line to flipping is getting the job done as quickly as possible and getting the property sold. Nowhere in here have I said anything about shoddy work, or whitewashing. True, that's what a lot of flippers do, but is not always the case, and never should be. But a delay in the work can affect the bottom line, because for every day the house is not sold, the bank clock keeps ticking, and the "profit" just slips away.

I guess if the investor is bringing ALL of the money, your share of the "profits" should probably be much lower, since you are being paid for you time and work and didn't bring anything to the table (money wise). He could find another inspector, and another GC to handle the job - he really doesn't need you.

You come from a stronger position of getting paid for what you are doing and walk away. There may not be a profit. The other side is: if the project loses money, will you share in the loss? I can see maybe getting a bonus for bringing the project in on time and under budget. An incentive for getting it done prior to the deadline. But share of the profits? I guess a lot would depend on what you were bringing in.

Hope it works out for you.
JF