I wouldn't negotiate on price any more until you see the bike.

One tactic is to take cash and when the guy is saying, "I've had lots of calls on this bike" and "A guy is coming to buy it tomorrow" just pull out six $100 bills and tell him you'll pay him $600 cash right now and take the bike. The seller will always be wondering if he turns you down will he ever get a better offer.

But don't buy it if there is something wrong with it OR if if it doesn't fit you. Keep that in mind always.