Most people in the Swap n Sell area will feel a LowBall is virtually ANY offer Less than their asking price, but a "REAL" Lowball is an extremely LOW offer (Way below a semi-established price on any item that has established USED selling price)
Example: an AMB transponder generally sells used for $70-80 U.S. - so if a guy lists one for $75.00/offer and somone replys - "I'll give you 20 bucks" - THAT's a LOWBALL offer.
Some get offended at Low price offers on items they personally have OVER Spent on - (But that doesn't mean it's a true Lowball offer)
I have bought a lot of stuff w/ Lowball Offers, but ONLY on things that don't really have an established USED Price, and usually on items that have been listed for several weeks, or even months w/o selling at the asking price. (Desperate sellers often TAKE what they can get - just to move an item)
Note: Generally if I am going to toss a "LOWBALL" offer on the table, it will be done as a "Hey, if you CAN'T sell this item for your asking price...and EVER get really desperate to move it - I'll give you x dollars for it at that time - "
Sometimes a seller will come back with a decent counter offer and we'll meet in the middle.