@William Allen Yes, you are correct in that buyer agents will typically only show a property with commissions at a certain level, which is understandable as they need to make a living. Most sellers that use a flat fee agent to list on the MLS still offer a market rate commission to buyer agents, which is why buyer agents still show their properties. There is typically no difference to the buyer agent in the amount they make when working flat fee sellers vs full-service brokers.
The other thing that I think is worth mentioning is that many listing agents, at least in California, have taken to the "pocket-listing" model where they try and keep their listings off the MLS so they can find a buyer themselves and double-end the deal. This is really bad for buyer agents as the inventory is not coming on market. Buyers are seeing homes they would have put an offer on being sold, and they are looking at their agents saying "Why didn't you tell me about this?", but the buyer agents never had a shot at it as it went under contract immediately because the listing agent found the buyer in advance.
What this all means for buyer agents is that the companies that are doing flat fee listings (such as mine) are their best friends. We bring inventory on market and don't try to keep it for ourselves. Meanwhile, their colleagues who are charging full-commissions are actually the ones hurting their business.
The truth is more complicated than meets the eye.
@John D. Yes, that's correct, the buyer would see the property come on market. The buyer agent isn’t obligated to show the property, but assuming the flat-fee seller is offering a market rate commission (as nearly all do), this is a no brainer for the buyer agent and another reason why the collusion argument is bogus.
The buyer agent could either:
A) Not show the property, to take a stand for the real estate industry to try and maintain 6% commissions for listing agents (who, btw, are doing "pocket listings" that are really hurting the buyer agents income - see my comment to William Allen above), hurt their relationship with their buyer in the process, and not make a buyer agent commission on the purchase, or
B) Show the property, which is the right thing for their buyer, and make a commission for themselves in the process.
I've never come across a buyer agent who wouldn't show a flat fee listing that was offering a fair commission. As you can see from above, it'd be a bit mind boggling for a buyer agent to avoid a flat fee listing in the name of protecting their bottom line. Pure flat-fee agents are actually bringing inventory on market (versus full-service agents who are trying to keep "pocket-listings" for themselves).