There's nothing "hard" about answering this question. The law forbids us from discussing it either amongst ourselves or with the public. Period. What's hard about that?
... and your suggestion that a buyer should "simply contact the home owner and tell them you would like to offer after the contract has expired with the agent" would not save them any money, as most agency contracts have a "protection period" of 3 mos, 6 mos, sometimes a year, for anyone who buys the property, who approached the property during the listing period.
... the "ethical" way for your buyer to do it, is to simply allow the listing to expire and THEN (and only then) approach the seller. Of course, that risks the possibility that the house may sell out from under them.
Any discussion of commission between Realtors (whether on a public forum, or on the back nine of the local golf course) could be considered an attempt to price-fix, and should be avoided. Even Kendall's innocuous "many agents I know of are asking X%, and X%" would be considered unacceptable when drawn before an anti-trust subcommittee.
Go for 0% commissions by refusing to deal with realtors and their delusions.
If a buyer simply contact the home owner and tell them you would like to offer after the contract has expired with the agent. Best deals to be had do not involve agents.
Like the others have said, it would be inappropriate for agents to discuss specific commissions in a public forum. But yes many would negotiate some consideration if a client were both buying and selling a property. Commissions on the sale & the purchase are inividually negotiable. You would negotiate the listing commission with your agent as your listing agent and again if you used them as your buyers agent as part of the buyer agency contract.
What you should do is ask friends, familiy, colleagues for recommendations of agents/brokers they've worked with recently that they've been pleased with. Interview several agents and discuss your scenario. Research the agents to check their other refrences, areas of expertise in the areas you are selling in and looking to purchase in. Interviewing several would give you the best idea of their pratices & suggestions.
Hope that helps,
As to the second part of your question, Agnes, I am unclear what you mean. Most agents work with both buyers and sellers, the notable exception being buyer-only brokers such as Buyer's Only.
I hope this helps. Please feel free to contact me with any further questions, although I must note that I can only advise you of real estate practice in New Jersey. A Massachusetts broker would be better situated to guide you in the peculiarities of real estate practice in Cape Cod.