In early 2018 I made a Table of Contents for the this website, creating several pages that could be accessed from the Main ToC.
One of those pages covered Mohel Standards, which included several subsections covering sterility and cleanliness. Here is the link specific to sterility.
The first time I addressed this is one of the first pieces of content in this website, Cleanliness and Efficiency, with some common sense ticket items to look for when hiring a mohel. Of course, most mohels fit these criteria (thank God - if they didn't it's hard to imagine they'd still be invited to perform brisses), but some can certainly raise the bar. That said, arm yourself with questions based on what you find there!