Try a search on the forum Craig as it has been talked about quite a few times.
A lot is going to depend on what sort of cover you are looking for, ie: will you keep customers vehicles overnight, what sort of limit you want on vehicle replacement/repairs. If you indent to drive the customers vehicles & if that’s on a public highway or just into your unit on a private estate.
There are specialist signmaking companies/policies about but I haven’t used them myself so can’t comment.
Mine has always been done through a local broker who I could meet with & explain exactly what I wanted. Never made a claim & that’s when you really find out just how good a company are lol.