Let's look at some widely-accepted definitions, from wikipedia.org:
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PIMP:  A pimp finds and manages clients for a prostitute, engaging them in prostitution, often street prostitution, in order to profit from their earnings. Typically, a pimp will force or pressure the women to stay with him; he may also protect them from other pimps or abusive clients. Pimping is a sex crime in most jurisdictions.  Often, pimps will initially present themselves as lovers or father-figures to women (who may be run-aways or otherwise lack a family network) before introducing them to prostitution and drug addiction. Most pimp-prostitute relationships are abusive, using psychological intimidation, manipulation and physical force to control the women in the "stable". Some pimps may not beat their prostitutes, as marks and bruises bring down both the price of a prostitute and the social status of her pimp.
See http://en.wikipedia.org/wiki/Pimp
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It is interesting that Wikipedia actually devotes a section under Shills to Online Message Boards:

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SHILLS:  In online discussion media, such as message boards, discussion forums, and newsgroups, shills may pose as independent experts, satisfied consumers, or “innocent” parties with specific opinions in order to further the interests of an organization in which they have an interest, such as a commercial vendor or special-interest group. For example, an employee of a company that produces a specific product may praise the product anonymously in a discussion forum or group in order to heighten and generate interest in that product, or a member or sympathizer of a special-interest group may pose as a highly-qualified expert in a specific field in order to give apparently disinterested support to whatever cause the group promotes.  In some jurisdictions and in some circumstances, this type of activity may be illegal. In addition, reputable organizations may prohibit their employees and other interested parties (contractors, agents, etc.) from participating in public forums or discussion groups in which a conflict of interest might arise, or will at least insist that their employees and agents refrain from participating in any way that might create a conflict of interest.
See http://en.wikipedia.org/wiki/Shill#Shills_on_message_boards
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The only "pimps" I've seen in this community are the agency owners/operators, and given the honorable way they appear to operate (with one exception noted last month) I would not apply the term to them.

We have, however, a lot of shills around here.  How many gentlemen have actually admitted to, and defended, preferred pricing and booking?  The problem is that they don't do so at the same time that they rave about the flavor of the week being touted.

In my opinion, the ethical thing to do is to put a note at the bottom of any mini-review or endorsement disclosing ANY special treatment you have gotten or expect to get from the person being discussed.  (This would include disclosing membership in a hobbyist group that has negotiated a price for you.)  In addition, I think it is completely fraudulent to post an endorsement giving the impression that you've had a session with a provider, if you haven't.

Just my $.02-worth.