I use the same low offer with cash method but with a twist. If they are asking say $1000 for a car and I'm willing to pay $700 I'll offer $500 cash but with an extra $100 cash in my wallet and then another $100 in my car, so $700 total. If they say "how about $800" then I can simply open my wallet, pretend to count, and say that I only have $600. If they don't take that and say "how about $700" then I can pretend to go looking through the car or if my girlfriend is there I pretend to ask her for the money and come back with the full amount. Allot of work but 75% of the time I've never had to go past the wallet!