When you vote to close something as a duplicate, Bicycles.SE automatically puts a comment saying that its a possible duplicate.
Is there a quick way of getting a comment on voting to close for product rec (or other close reasons)?
When you vote to close a question as Off Topic, there are a couple of options presented. One of those options is to automatically add the comment:
"Questions seeking product/service/learning material recommendations or item valuations are off-topic because they tend to become obsolete quickly. Instead describe the situation or specific problem you are trying to solve, or try chatting about it in The Velodrome."
When the question has garnered enough close votes, the associated comment of the closure reason that has the most votes is then automatically added to the question. In essence, the "product rec" message works the same way as the "duplicate" message.