I have no idea what these points are that you mention, but Best Offers are private between you and your bidder.
Heck, no one can even see who is bidding against them. Only the seller sees who is bidding.
But if you have one listing for 450 items/points and you sell off 150 of those items/points, then you have to end the entire auction AFTER cancelling all the other bids.
If you don't cancel all the other bids, then the high bidder at the time the auction is ended wins at the current high bid. And that bidder will expect to win all 450 doomahinkeys.
And if you sell the 150 points, all those bidders who were cancelled are unlikely to return to bid on the remaining 300.
I would suggest that you tell the guy who is negotiating to bid or not bid. Your auction is for all 450 points and you have other bidders.
BTW, you should be aware that new sellers, especially those who have never even bought anything on eBay, are fresh meat for all kinds of scammers. Be very wary. I am not very knowledgeable about timeshares or eBay Real Estate, but your Seller Protection in that category is very weak.
It's been a long time since Patience shot me and that was due to a perfectly legitimate conflict of interest. I got no grudge.- Captain Malcolm Reynolds