@Roger G.
In situations like this, I will try to get the FHA appraisal removed the property. Sounds like you have a good case since they discounted a bathroom when it sounds like they should have counted it. You could get the tax records changed to show the bathroom? Any future FHA offers on this property you could argue the appraisal was done wrong because of the bathroom. Some lenders will go to bat for you on this stuff (they want to get paid too.)
I also keep notes of which lenders use "strict" appraisers, I won't accept future offers from that lender. When do you a lot of flips, you will find quickly which lenders are not flip friendly. I try to get to them use my lender by paying for the appraisal and they close FHA and VA loans in 2-3 weeks.
If you are not doing so, you should also be sending the appraiser any comps you like and total remodel costs. I've found this to be useful. They will likely come back with any questions about the house and we can get them addressed before its "permanent". I've had them ask for additional costs, comps ,etc to help get a house appraised. Treat them like a team member, not an enemy.
I think ignoring all offers that are FHA, VA, USDA is a bad move for a couple reasons:
1. You are more likely to get multiple offers which greatly enhances your negotiating power.
2. If you control the process better, you should be able to avoid low appraisals. (providing comps, remodel costs, using your list of preferred lenders, etc).
I hope this helps, good luck!