I think the question you need to ask is whether these are natural or you're involved in a link scheme. If the plumber is writing about other reliable contractors in the area and links to the garage door site in a resources page, then it could be OK. It all depends on context.
New advertising option:
A review of your product or service posted by a Sterling Sky employee. This will also be shared on the Sterling Sky & LSF Twitter accounts, our Facebook group, LinkedIn, and both newsletters.