If you would like to get more information about a product you saw online, here is a template you can use to write an inquiry email for product information.
Hope this email finds you well. I came across your [product/goods] [online/newspaper/classifieds/social media etc]. Is it still available?
If the answer is yes, I would like to schedule a time and date so we can meet up. Your item is something I definitely need.
Looking forward to having a chat with you about it soon.