I had three >$100 items bookmarked for Prime Day...

[rcjordan]

...none of them went on sale. Crap!

One item $80 item dropped to $69 the week prior (I bought it) but went to a new, slightly higher price on Prime Day.

[Travoli]

This is one of the reasons I use the Keepa plugin. Shows a price history chart right on the Amazon.com product page. E-mails me if my price target is hit. I believe there are other, similar, free services.