Observationally, their model was roughly like this:

* For hit movies buy an obscene number of copies to rent month 1

* Sell off some for a discount as the rentals dwindled

* Discount anything over a reasonable backlog / duplicates set shortly after

Offhand I think they tried to time this to end well enough before the release windows slid to TV + Ads distribution.

* Rent the backlog until dead or until they sold in a discount bin

Some independent shops also competed. I recall my parents kindly rented a few less popular games they happened to carry. Not sure about videos, might have been better for stuff not mainstream enough at the big national chain.