how it's worked in previous years is that the top 150 bids will win, in event of a tie, like let's say 141-152 all bid $150...then the folks that bid earlier will be ahead of those that bid later, so it's a combo of who pays the most, and in event of a tie, who bid first
what's fun to watch, depending on your definition of fun, is the last hour it closes....just hit refresh every 5 minutes and watch the bids climb
traditionally also, the tours are early sun am, as in leave the hotel by 8am and they have been open to all ticket holders
now that has been previous years, check the site for details for this year's presuming it does happen