[quote name='Stacker' timestamp='1355652979' post='1900859']
A low offer, to me, has to be several hundred pounds below my asking price. [/quote]
Not if the item in question is priced at, say, £3500. An offer of £3000 may well be accepted depending on the condition, age, reason for sale, etc.
As stated earlier, I generally think that less than 50% of the asking price is a low-ball. But it depends on the asking price!