I just noticed after posting in the for sale section that I am not allowed to respond to the other offerings. There was nothing I wanted to respond to, but this got my curiosity up so I read all the rules that I could find and found nothing about responding to ads. Yes my eye sight is failing. If it is a question of establishing trust why would a seller be trusted more than a buyer? Nice site in any event.
I think the way buying and selling is treated on here is annoyingly restrictive but the way you "respond" to an advertisement is to send the seller a private message by clicking on their name and then "Start a Conversation".
Here is the rules, the top sticky in the 'For Sale Forum" https://www.cointalk.com/threads/hey-read-this-before-posting-here-for-sale-forum-rules.190428/ And the reason for the 'annoying restrictive' ( as it was called) process is that people were not 'nice' in many cases when replying was allowed, and the decision was to not have advertising at all, or to restrict it to prevent flame wars and legalistic threats. So it is restricted by owner's choice. Jim