eBay is my second job, and I can confirm that there is NO LEGITIMATE WAY for any seller to find out what your highest bid is before the auction ends. It is not possible.
I have had many auctions end with me winning at my exact highest bid. As Bill pointed out, this is because someone bid just below me at the last second and pushed my winning bid to its max based on the increment for that pricepoint.
I think shilling, much like scalping in the toy community, is one of those things that is grossly overhyped. It does happen, I'm sure, but there is always an inherent risk that comes with not knowing how much to bid without going OVER the highest bid. I can't speak to "hacking" and so forth but I suspect eBay, like Google, has an entire team of super-geeks paid to figure out all that stuff.