Make sellers send ahrefs traffic screen shot for guest posts links.

Can there be a rule in place where sellers need to send a ahrefs screenshot which shows traffic of the site to their buyers, as not all have access to ahrefs and this way a buyer will know if he’s being sold a product as per what the seller has advertised in his guest post bst?

Absolutely IF the seller has listed an ahrefs report as part of their service then they should include it.

Sellers can offer ahrefs reports as part of their service, if offered - then they should absolutely include it as part of their deliverable - if they don't and it's something you require to make your buying decision then ask the seller for it before you place the order. If they can't / won't provide it that's not the seller for you based on your criteria - you either adjust your criteria or move on to the next seller.

If you have a very specific set of requirements then try placing something in the want to buy or hire a freelancer section depending on your needs.