IMO, things like this should not be posted in a wanted post that was started by someone else.
If someone is reading thru another persons wanted post and they see something that they are interested in buying or making an offer on, they should use the forum's "Conversation" (PM) method to contact the person who has made the offer.
To start a Conversation hold your cursor over the person who you want to send it to's name. Click on Start a Conversation. Give it a title. Write whatever you want to say. Click the Start a Conversation button at the bottom of the page.
I think in cases like this, whoever made the offer is somewhat obligated to give the initial poster who started the ad, first dibs.