Supporting vendors pay for the considerable bandwidth charges on the Forum, making it free for the rest of us. In exchange, they get the privilege of using the Forum to market and promote their goods and services.
Forum members are welcome to sell a sportbike or sportbike parts they purchased for their own personal use. Anything else is considered to be a commercial sale. If the sale is appropriate for the Forum, post it on the Forum, rather than linking to it elsewhere.
Members are not prohibited from mentioning it when they have a good (or bad, for that matter) experience with a non-supporting vendor. But such mentions cannot be so specific (addresss, phone number, e-mail address, URL, price, part number, etc.) and so frequent that they become marketing and promotional references.
Members can include a mention of their personal businesses in their signatures so long as the enterprise does not compete with an existing supporting vendor, is not sportbike-related and is not so detailed or so frequently appended to their posts that it becomes inappropriate marketing and promotion.