1) Professional buyers are defined as any person not kin or well known to the seller that has bought another property within the last 3 years.
2) Professional buyers contracts must allow a 30 day cooling off period in which the seller may back away from the agreement without punishment.
3) The 30 day cooling off period is initiated by the buyer prominently posting the offer in the local MLS service or similar prominent and accessible system. The buyer is responsible for ensuring any alternative offers during this period are conveyed to the seller.
4) The buyer and seller may avoid the 30 day cooling period by having a certified appraiser conduct an appraisal of the property and executing the sale at no less than 6% below appraised value.
I could throw in a couple other clauses in there to take care of people "brokering" regular sales to straw buyer or about requiring disclosures that recommend sellers consult with family and/or homeowner advocacy group within the 30 day cooling off period, but that is the crux of it.
This wouldn't eliminate the industry, but it would limit the actions of the worst offenders. Offers dramatically below market value should get counters. The worst consequence seems like it would be that the seller will get absolutely swarmed by realtors trying to convince them how much more money they would get with them.