I don't know what you consider a low ball offer but I usually make brutally low offers on liquidator's equipment because usually it's so overpriced.
I usually start at a max of 10%~20% of the asking price and go from there, unless of course I see a stellar deal that I'm sure will be snapped up very quickly.
For example, I've seen liquidators list 2465Bs for $1000 and I'll offer $125 and they have accepted.
Many liquidators have no idea of the value and they simply go on ebay and list their stuff for the highest price they can see.
Good luck with your TDS784C. You may eventually need to convert to LCD because those shutter type LCD/CRTs will eventually fail.