regarding your both your items
1) people here are smart enough to know what they want to pay. a broker won't manage to sell for than the market price on this forum more just because they need to take a cut. this is basics of supply/demand 101. and furthermore, most likely the broker is buying from or selling to someone (such as a friend or aquainatance) that doesn't have access or credibility to trade on this forum, hence they would maybe buy for much cheaper or sell for much more. so the money thing is not a concern.
2) why do you think it would be any different if something goes wrong and its not a broker? on the contrary, a broker would need to keep up their reputation rather than a one time buyer/seller in this chat. think about it.
Well couple things and I assume you are a broker
1) You have a point on brokers having more access and are probably sourcing from another source that is not available. Brokers also provide additional access and also additional liquidity. so given
2) Dealing with a well established member who has his own her account in definitely better than dealing with a broker. I am not comparing to a one time individual use.
3) Many broker are not transparent that they are brokers. I have had several people here lie that "it's for a friend " and I know they are a broker. This is even worse behavior . Actively not being transparent is one thing. Lying about it is another
4) A broker will have his reputation but if you are dealing with an established individual he will be concerned about his account. And it's not like the broker is a lawyer with reputation that would be damaged.. If he loses his reputation they go do their rate on another forum. Most of the brokers here are anonymous so we don't even know who they are. Many of the have several handles . So I don't buy this argument at all.
Bottom line is brokers are useful and provide value. Do I deal with them - Yes. once in a while when I need to. Do I prefer to do a deal with an informed individual over a broker - absolutely every time even if it means it costs me a little more