Product managers and UX engineers are there to do product management or UX design, not to filter information from the rest of the company to programmers. That means that most of sales requests are better forwarded to a product manager or UX designer, but there is nothing stopping them from directly filing a bug report to a developer and chatting about potential fixes/timelines etc. Also if some feature is important the product manager can just tell them to talk directly with the relevant engineer to get the feature done.