When I saw your post I thought you would have trouble.

You can't talk about chips until they are in your hand.

I can tell you what likely happened… it happened to me. Someone sees your post, says… hum… let me do a completed auction search.
They find the auction that you won and then they email the seller saying… WOW I'm sorry I missed out on the auction you had. I'd be willing to pay
x times what you sold it for. That is the "nice" way of screwing you. I've also seen other collectors who are just bitter rats do worse.
They will email sellers just to sabotage your good buy, with their "generous" knowledge and to tell them how bad they just screwed themselves…ext.

I bought a very valuable chip a while back on ebay for a small buy it now price. I said nothing to anyone. The next day a person on this board posted a link to the closed auction and made a post like… "WOW I wish I would have seen this one". Well…. long story short. The seller was flooded with emails from club members who saw the post here. They asked if she had more chips to sell, and said that they would be willing to pay way more for them, way better than what she just sold it for. The auction ended on Sunday and there was a holiday Monday when the post was made so there was no time for the seller to mail out at the post office. I knew I was screwed the minute I saw the post here. Like you… I got a similar email from the seller saying she wanted to cancel the transaction. I asked her to call me. We spoke on the phone and she said she was sick to her stomach all night over everything. I offered a compromise… I offered to pay an amount that we both felt was fair given the situation and she would send the chip. We were ok with it.

Here is the kicker…

The reason she was sick was because she had printed her own shipping and had already put it in the mail drop at the PO sunday. lol… Priceless…

The seller forwarded me every email she got from people who emailed her through ebay including some that were pretty embarrassing. If I were you I would try and see who those helpful folks were who killed your deal. Some people just can't see someone else get a good deal on something without reacting.
Sorry you had to go through it. Live and learn… There will be bigger finds to come. Just don't post about them till they are at your doorstep.