Yes. In the UK they go up a month before, because we have consumer protection laws that required retailers of e.g. white goods to have maintained the higher price for any announced discount for at least a month. So you knew that sellers thought there would be (at that point unannounced) Deal Days, because the prices of some things went up 20% back at the beginning of September.

There's https://camelcamelcamel.com to check how prices developed.

There's still the possibility of shenanigans with different models that can be overpriced for long so they look like a good deal when they get a normal price

I had ordered a new wireless charger about two weeks ago (without Prime). a day or two before it was meant to be shipped (about a week before Prime day), my order was cancelled "due to lack of stock". I go to the original product page and what do you know, it's in stock but $3 more expensive. Looking again today, it's on the Prime sale for the old price.

Scummy behaviour at best, and illegal at worst.

The warehousing industry, and it is counting all "serious" injuries (which basically means an injury that puts you out of work for any amount of time or requires you to be reassigned to a different job).