Trademark poaching being considered as a loss of revenues by affiliate program owners, procedures and services have been set-up to fight it.
Merchants can identify trademark poachers by detecting unusual high conversion rates or affiliates who rise too quickly in volume. They can also look for search engine referral URLs, but good poachers do URLs laudering.
Affiliate networks can search for the same evidences and use internal black lists.
Some outsourced services can also provide specialized detection services. Some are "pure" poaching detection services and others are broader trademark protection services.
For techniques used by poachers, see trademark poaching.
Brand Verity offer a service specialized in trademark poaching detection: