I always explain brokerage as being like an estate agency with a bit of conveyancing mixed in. A broker simply finds a buyer and 'introduces' them to the vendor, playing the part of the intermediary throughout the sale, handling the money transfer and ensuring the paperwork is completed.
Brokers cannot agree the selling price, they can only pass on the offer to the vendor who then decides to either accept or reject; whereas dealers are selling their own asset and can decide without consultation to accept or reject an offer.
Because the broker is only being paid a commision for finding a buyer, and the vendor isn't selling as part of a business, then there are no consumer rights attributed to the buyer/purchaser. It is pretty much the same as buying privately.
The bit where the broker handles the money transfer is the bit where the private seller is most at risk. Not a risk I would take, personally. This is why solicitors (not the Agent) handle the money on a house sale, because their client is 100% protected financially.
If I was using a broker (including a dealer selling on commission) I would insist that my money is properly protected. There are various ways of doing this but the broker / dealer collecting full payment from the buyer isn't one of them.