Research for Sean Howe’s Marvel Comics: The Untold Story has dug up a lot of long-forgotten dirt, but here’s a particularly sad one: Marvel selling art by Romita, Sinnott, Kane, Sal Buscema, and more to a Winnipeg art gallery for $1000:
Marvel began returning current pages to artists sometime in 1974, and eventually worked retroactively back a few months, to comics cover-dated from January 1974; among the earliest issues from which art was sent back were Avengers #119 and Amazing Spider-Man #128.
But a year earlier, Marvel sold the covers to these issues, cover-dated January 1973, to the Winnipeg Art Gallery. Seven covers, plus progressive proofs and color guides for each, for a total of $1000.
Back in 1986, Irene Vartanoff (who began managing artwork return in 1975) told The Comics Journal that Marvel would occasionally send artwork to exhibits. But as far as I know, this is the only evidence that exists of Marvel actually accepting money for pages of original art.
Ownership of Marvel’s artwork was a huge issue throughout the ’70s, with most being returned to the original artists after they signed a release, but only after 1000s of pages had been stolen, lost, or…maybe even sold.