The lender will most likely not bid above fair market value which is most probably less than what would make the lender whole. If he purchased at a price that would make him whole, he would then be faced at selling at the market value which would be less than the price he paid for it and also entail additional fees and carrying costs. Most likely the lender would not bid to fair market value unless he felt that the market represented a case for sudden revival.
The lender will most likely not bid above fair market value which is most probably less than what would make the lender whole.
You may be correct if the sheriff is conducting an open auction. In that case, the lender will have no reason to preclude a winning bid from a third party. If it is a blind auction, the lender will submit a bid that is consistent with the balance of the defaulted debt, purchase the home and proceed with marketing the REO.