My advice to you would be: leave as little room as possible for surprises. Be proactive and communicate with your customer rep what exactly they will be doing at your plant/site. You could ask for an agenda/schedule. Information on what documents and any processes they are interested in seeing, etc...
One never knows for sure the reason for the "visit", if you don't ask. It could be for something as simple as they having to perform some supplier audits, based on their schedule. Or, it could have been triggered due to quality problems. Either way, you are entitled to know some basic information. Do ask.
As a supplier, you have to balance the need to keep their confidence in you with the need to protect proprietary information or data that could be misused against your company.
One never knows for sure the reason for the "visit", if you don't ask. It could be for something as simple as they having to perform some supplier audits, based on their schedule. Or, it could have been triggered due to quality problems. Either way, you are entitled to know some basic information. Do ask.
As a supplier, you have to balance the need to keep their confidence in you with the need to protect proprietary information or data that could be misused against your company.