Swallens would buy overstock from distributors. The Timex/Sinclair ZX-81 was still for sale for another six months before they were dumped for $10. You had to be careful what you bought there. They were known to find a couple hundred 10 year old color TVs still in the crates, and not tell people that there was no factory warranty. They would also sell tube type TVs as solid state. By the time they needed repaired, it was too late to take it back.
Those magazine ads were usually two months or more behind in the current prices, due to the time required to hand set the pages, print & assemble the magazines, and distribute them.
I guess that you've never heard of a 'Loss Leader'? SS Kresgie's 'Five & Dime' was started that way. Sell some cheap items at a loss to get people in the store. Today they are called Kmart.