would it be possible to transform this module into a Flags integration?
there a similar module, Not for sale which uses this approach.
check these 2 issues on it:
Flags API v2 problem solved: http://drupal.org/node/908358
behave like Out of Stock: http://drupal.org/node/908364
oops my bad
Probably not for now, but will try to investigate if this is actually needed.
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