For sale new heater core for 1973 thru 1977 Pontiac Grand Prix without
factory air conditioning,

Yahoo URL snipped.

Why would anyone buy something like this when they could walk in the local
parts store and get it cheaper and no shipping fees?

From Advance Auto Parts's site:

Part No.
399070 GO/DAN Heater Core
Heater Core: w/o AC
Warranty: Lifetime Limited Warranty
$23.48

Part No.
399071 GO/DAN Heater Core
Heater Core: w/AC
Warranty: Lifetime Limited Warranty
$17.97

I wonder how Yahoo feels about commercial sellers spamming.  Ah, it appears
they don't like it.

Using or causing to be used Yahoo! computer systems to facilitate the
transmission of unsolicited or unauthorized material. This includes any
promotional materials, URLs, "junk mail," "chain letters," "pyramid
schemes," or any other form of unauthorized solicitation that you may
upload, post, email, transmit, or otherwise make available.