In the state of New Jersey, commissions are negotiable between the seller and agent. In the current market characterized by excess inventory, agents are using the commission compensation to distinguish their listings. Since most properties are not sold by the listing agent but by a cooperating agent from a different brokerage, a larger commission can result in greater compensation to the cooperating agent by a larger commission split. Accordingly, most agents I know of are asking 6%, but 7% or even 8% is not unheard of. A listing priced at 5% is disadvantaged in the current market relative to comparable inventory.
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.