If you go to Google Product Search and change your settings to turn off Google Instant and show 100 results per page, you will be out of luck.
Similar to the settings bug on Google News, where you can't set the search results to open in a new window when clicked on - here you can't show 100 results per page when you change your search settings.
The report comes from a frustrated CyberMonday shopper in the Google Web Search Help forum. He said:
The Google Shopping page has started to return only 10 results at a time. This happens regardless of the browser or OS used, and happens even if you set Instant Search OFF and Display Results to 100.
Even worse, if your search finds, say, 1,000 hits, the Shopping engine will only let you see ~30 of those, ten at a time. There is no way to get to the rest.
This makes what was a very useful utility essentially useless!
Yep, it does make that feature useless. I tested it myself and yes, I can reproduce the bug.
Forum discussion at Google Web Search Help.