In other words, after you successfully sell a particular job at a particular price point, at a previously agreed upon rate of commission, the boss wants to renege on the promised commission and steal the money from you and take it for himself.
Sorry if I'm talking too bluntly here; messing with sales peoples' commissions is the classic problem that sales people have. He is not even trying to be clever about it.
Usually what happens with really good sales people is that they'll agree to work for a company at a given commission rate. Previous sales people in the same position had dismal sales to their credit, as a matter of routine. So the new guy comes in, uses an entirely different approach, and just blows up previously existing sales records, and does so continuously. People at the top see this guy getting paid enormous sums of money, probably even more than they get paid, and it really pisses them off. So the first thing they think of doing is to cut the rate of commission they'd previously agreed to pay the guy. Or they take away a sales territory that he's got all slicked up and selling like gangbusters, and give it to one of their buddies. Anything to keep this ass-kicking saleman from making irritatingly large amounts of money.
What they don't understand is that for this sales guy to be making irritatingly large amounts of money, the company also has to be making huge amounts of money, too. It is communist thinking that is the problem. They end up doing everything they can to remove all of the incentive to sell products or services from the gunslinger they hired in the first place to do just that. They in effect kill the goose that laid the golden egg.
Your boss is not even smart enough to give you the money he's already agreed upon for the deals you've already done, and then next week announce a change in the commission structure for any future sales going forward. He just steals the money from you right now, no excuses. At least, that's the way I'm reading the situation you're describing.
To me, (and I know this sounds really harsh, coming from a guy who's not a pro) it means your boss is a really stupid, shortsighted individual. He deserves to have you give up entirely on the whole idea of being a sales rep for the company.
Treehead32, on the other hand, seems like the dream boss from a parallel universe, or something. To be willing to pay climbers their full rate of pay while they are selling, plus commission on top of it when successful, is just incredible. His approach ensures the security of the earnings of the climbers, and also gives them insight into just how hard it really is to sell, and the consequences of selling services too cheaply.
I think you should absolutely insist on being paid all of the money your boss owes you for your previously earned commissions. Then ask him if he doesn't think it's fair, what rate of commission would be fair? Then when he tries to cut your commission rate in half, you tell him that that is not enough compensation to get you to even try to do sales, thanks anyway, I think I'll just stick to the climbing.
It is no wonder he's the one responsible for most of the sales; he steals from anyone else who tries.
Apologies for the rant.
Tim