The opposite of "putting for sale" can be described in a few different ways, depending on the context. If someone is taking something off the market or withdrawing it from sale, the antonym could be "withdrawing from sale," "removing from the market," or "taking off the market." On the other hand, if someone is acquiring items or accumulating them for themselves, the antonym might be "stockpiling," "hoarding," or "collecting." Additionally, if someone is simply not engaging in commerce or selling anything, the antonym could be "non-commercial," "uninterested in sales," or "inactive in the marketplace." Whatever the opposite term may be, it is clear that it stands in stark contrast to the act of "putting for sale.