It seems unfair to me to negotiate on the side with another potential bidder.
Sometimes shipping isn't fair. I sold something recently that was $8.00 to ship within NY and over $12 to ship to Alaska. Since many people put the higher shipping in their auction, they may be very willing to lower the cost of shipping, if it isn't going to cost them the full amount. For me it doesn't matter if I have bids or not...I don't "make" money on my shipping, and if I can be more fair with the cost, if someone lives closer, then I'll lower the shipping price. eBay is an individual thing..each have to decide for themselves what works best. I've bid way higher than I meant too, when the seller has worked with me, so in the end, it was a positive experience for both of us. While I don't mind paying a lot for an item if I really want it, I admit I would be miffed to find out, not only did I spend a lot fo the item, but I paid way more than their cost to ship/package (again, I'm talking general here..not your items).
I still would be following eBay's rules as far as the bidding goes (highest bid wins)..however, whatever deal you make with the shipping is between you and another..eBay stays right out of it, unless it becomes very obvious it's fee avoidance. Sometimes I have offered to lower shipping, before I used the table for them to figure it out for themselves. I used to charge what my highest shipping was, but when I found out where they lived, I lowered it, before they paid, or before they bid, if they emailed me. Sometimes people will ask if we could meet (which I would rather not do) to exchange the item, and they pay no shipping at all. That saved a local bidder a ton on a table saw when he asked if he could come to our home to pick it up...and I thought it was very fair. I got what I wanted, they saved money...lots of money. I think they may have bid higher, once we made that arrangement (because they actually picked it up from my house, I didn't have to drag it anywhere).
Doris