You can list items with the buy it now price, and also mention OBO in your CPF sales ad....
I very much prefer to use a system which allows flexible options within the structure of an 'auction' format. I gather that things are listed on this site as (in essense) a 'buy it now' price listing - period, and that's a pretty restrictive method for me. If I could at least list a 'buy it now' price, but could optionally have an 'OBO' added to that, I'd probably go for it. I don't think that option is provided for here(?). I'm aware of the rather laborious serial 'price drop' posts which are apparently used here. I find that a bit tedious.
These are offered as 'as is' opinions
Other members would then PM You with their offer. Of course if an offer is accepted by the seller,
It is up to the seller top update their listing(s) as sold, so that others do not send payment for an item
that can not be fulfilled, and leaves You having to refund monies to someone that paid for an item that
is no longer available. Just my $0.02.