It is not allowed in auction regulations to give an estimate lower than the reserve price so that is why they will not accept a bid lower than the lower estimate. The lower estimate can be higher than the reserve, but not lower. Holt's policy is to always set the lower estimate on the reserve (if there is one). Occasionally in their live Main Sale, they do accept bids lower than the lower estimate and this reflects the lack of any reserve, eg. deceased estate.