I would suggest being tenacious...I think that's something sellers can sense. Before I make a purchase decision, I analyze the price. There's a "list", "discount", and "street" price. The Street Price is FMV, or rock bottom "I gotta sell it now" price. If I'm not saving at least $5-$10 or more from the "street" price, I'm not getting a bargain, because someone on the street can give me the same thing. My mind is made up.
(With computers, "PriceWatch" always provides a reliable "street price" for any component. I've always wondered what the equivalent auto supply "PriceWatch" would be. Any ideas?)
Folks here have given me some very good online parts store addresses, and often, eBay Motors can provide some pretty good prices on items previously sold. So I'll take those rock-bottom prices and start looking for deals. I know when I say, "I can get a set of Edelbrock Elite valve covers for $40," I can actually do that. If the seller is wanting to sell instead of getting a suntan, he or she should be willing to knock something off the price, in which case you get a deal, even if its only $2.00 less.
I try to prioritize and memorize my build/mod plan. That way, I'm not distracted by everything, and I have a solid idea of what I need most, and also the lowest price on the street. Then if I find someone whose prices are "in the ballpark," I'll hit on that seller first with one of my high-priority, mid-ticket items (right now, for example, I'll be looking for a good, deeper-than-stock, oil pan). If he/she is willing to "play ball," I pull a couple more prioritized items out of my memory and work up a good "package deal", which makes the seller more relaxed and willing to cut a break. While "dealing" I also keep an eye on the TOTAL cost I will end up paying for the lot which gives you a little wiggle room if the seller is high on one or two items.
But I stick to the bottom line pricing...in order for it to be a deal, it has to be less than street. Its easy enough to walk away.