If they don't say firm then expect them to come down some unless they have a lot of interest. Some people don't feel comfortable with negotiation. If I say obo I expect someone to start at least lower and go from there. If you make an offer or $3600 on a $4300 ask you are not going to upset anyone but you might get the pin for 4k or the seller will respond on what he will take. I think it would surprise a seller more to get an offer at asking price then one starting lower to begin with having a "obo" tag.

My definition of a "low baller" is someone who never plans on buying the pin unless they steal it. If someone really wants to purchase a pin but comes in low then works to the sellers desired price "shrewd buyer".