I wouldn’t say there is a slow down. There are probably multiple reasons that maybe not as many sales just this week alone, such as SDCC or summer time/back to school prep. But overall I don’t think it’s that much different.
IMHO most of the time a significant change in sales activity is due to the books being offered. For example Oceanmills and Kryptomayor both had large threads with affordable books and as expected, sold well. Reasonable prices, great sellers, good number of titles - all that leads to sales. Same with GACollectible’s big modern thread with low prices and lots of books, it had good sell through. Single books or handfuls of books, which sometimes are priced reasonably, sometimes not, just don’t have the large draw of buyers. And of course if it is a few single key books, the boards have always been notorious for a place where people will wait and only buy when the selling price is below the market enough to make money for the buyer.