We often feel 'silly', 'uninformed', or just plain 'ignorant' if we have questions about a process or product that we think we should know ALL about!
I know that I used to suffer from that! But in an age where products, concepts and information is changing rapidly before our eyes on a global platform - it is impossible to feel like we knew as much as we could have 10-15 years ago.
Questions from one customer should raise a red flag to you that other (potential) customers are thinking the same thing, but are not asking!
Sometimes what we are offering is full of assumed knowledge. Sometimes it is ok - for eg: the tab at the top or bottom of a web site that says 'Contact'. We don't necessarily need to add 'Us' to the tab - it is assumed that when you hit the Contact tab you will go to a page where you can contact the company.
Never begrudge those questions, listen keenly & rewrite what you need to rewrite. Offer more information or images if need be. This will help you capture the potential customer / client the first time round.
Remember, not everyone asks questions - and if one has, then many have thought about it.