How to communicate a viewing

Hello open-all-hours. If you are happy to do so, you can inform potential buyers that they can view before paying without obligation if they are the winner or purchase the item with buynow. You can't leave contact details in your description or in Q&A

Apart from that have an accurate full description and lots of relevant photos. 

EDIT TO SAY: This is assuming you are talking about a standard marketplace listing. Some items across pets, real estate, motors, service listings do allow you to publish contact details.