I think google is trying hard to send visitors they think are likely to buy directly to the stores that yield the best user satisfaction. Affiliate sites are being hit hard in terms of traffic loss as of late, well, not counting Google's prominent offers.
Does your site feature a brick and mortar business address prominently displayed on page? It might be good SEO if it did and it would be even better for your products to provide ratings for Google to data-mine from.
Mayday could have been when this was turned on.