It can take as little as week or as long as a month for girls to start laying regular after a BIG change in environment. Some will get thrown off by moving to a new coop across the yard. Others won't. But every adult hen I've ever had, took a couple weeks to get going again depending on what situation I took them out of. Two hens, came from cramped quarters and awful roosters. Took them 3 weeks. Two other hens, great space and place, took them each 4-5 days.
But, if age is a factor, how big are the eggs? Did you spot who laid what one from the couple eggs you did get?
Were you looking to sell the eggs for hatching and remake some money back? If that was a goal, I would set every egg they popped out into the incubator, and see if you could create a new flock for next year. Either their laying will improve, or you'll be able to scavenge enough to start a new flock.
I would be pretty ticked off after a couple of months and still no improvement or natural reasons of why they're not laying, such as molt. I'd be setting every egg I got in hopes making a new flock from them.
But with the nature of these sales... what can you do? I just bought two Flemish Giant doe kits, and yesterday when I was playing with them, I started to notice very key differences between them, yes, they're the same color. But size, face shape, ear shape, I started noticing all that, and one I'll bet is a cross and not purebred. So I got 1 1/2 Flemish Giants, when I paid for two. Luckily I didn't pay for pedigreed and more expensive bunnies, I won't do that unless they have a tattoo as proof. He had a set of breeding bunnies too, for $250. I didn't know the guy well enough to spend all that.
It's risky buying from strangers, even if they have a good reputation. Have you tried contacting them and seeing if they have explanations/excuses and maybe even a resolution?
It makes sense that they would have sold these birds when they noticed a decrease in laying, so they decided to let them go. You can contact them and see what they say, it was a lot of money. Or make lemonade, and hatch every egg you get. I'd keep on hatching until I felt I got my monies worth in chicks. Because if they lied, and made the sale under false pretenses, you can bet they'll be hard to deal with and they'll either ignore your calls/emails, claim innocence, that whole ridiculous thing lying sellers do after their lies are known. It's not quite enough money to take them to court or anything.