I've sold a lot of horses over the years and treasure my "return customers". I would not consider telling "part of the truth" to a returning client or anyone else. All or nothing. I would see this as an "implied warrenty" of the horse's condition when "some" of the problems were revealed, but not something as important and significant as a previous laminitis bout while knowing the horse is a resale project!! I think "that" info should have been revealed to any buyer. Return or not!!
Posting this situation on a public forum does lack good judgement, though.
Added: Note to self...read all the way through the thread before commenting!!! I stand by what I originally posted, but the OP was not 100% truthful in her first post. The "other party's" explanation really fogs up the facts, but IMO this should all be done privately...not on a public forum!!! Regardless of the entertainment factor to all un-connected parties!!!