At Christmas time people all over the world have gift exchanges, whether for family, at the office, or within a group.
Well, I discovered that the Genealogy world also has exchanges of a sort - there are many sites that host Certificate Exchanges. If you buy a BMD certificate by mistake, that is not relevant to your family, you can offer it to someone else. These sites are just hosts - you have to contact the certificate holder directly, or leave a contact email for people to contact you if you are offering.
You may find more links that are perhaps more local rather than national by doing a search using keywords: certificate exchange bmd. You can also add "~genealogy" to narrow the search.
I didn't find one specifically for the USA, if anyone knows of one I will add it to the list.
Check these sites before you buy BMD certificates.
Canada BMD Exchange - at olive Tree
Benelux - Belgium / Netherlands / Luxemburg - Certificate Exchange
Certificate Exchange - UK
Scotland BMD Exchange
Australia BMD Exchange
BMD Share UK
Ireland Certificate Exchange