While the sex of an animal isn't going to change, regardless of whether the period is 2 weeks, 2 months, or 2 years, there are some other factors to consider (especially given the current climate):
1) Many of the people offering great deals on "correctly sexed" animals probably won't even be around in a year or two...good luck on somebody making good after they've given up on the hobby/business (though a select few would undoubtedly still make a reasonable effort).
2) Money concerns are already an issue for many people. Look how many people are selling off critters just to pay bills...those funds are gone in short order. How many times do we see that, and statements to the effect of
I can't give you what I don't have, on the BOI?
3) The volatility of the market also bears consideration. What sold for $1000 just a couple years ago, in many cases, is down to 25% of that. Heck, I've seen prices drop 50% just over the span of 6 months. That has nothing to do with the seller not getting what was paid for...but it is certainly a factor in resolution. What is deemed an acceptable effort will depend on the people and animals involved.
As I've mentioned - I have received several missexed snakes over the years, and the responses have varied. One person, contacted within two weeks of purchase, insisted that I was mistaken, and "guaranteed" I received a 1.1 pair (it was 2.0, and I got nothing). One person I notified, just for informational purposes, several months later; and he offered to get me a replacement (I declined, because my male was actually a female). Other times, I didn't even bother notifying the person because of the elapsed time - if I had spent $3000, and received a male instead of a female, I don't know that I would have been able to shrug it off as easily....so I guess, for me, AS A BUYER, price is also a factor. A $250 animal isn't likely to be worth the aggravation for me, if I didn't confirm the gender in a "reasonable" time. If I check within said reasonable time, though, I'd be clamoring for either the right snake or my money.
When the situation was reversed, and I sent an incorrectly sexed snake, I made every effort to make it right....or course, the customer wasn't carrying on cursing at, and threatening, me at a show, either
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All said, while the seller is responsible for correctly identifying the gender of the animals sold, I do feel that the buyer should shoulder some responsibility by confirming that the received animal IS what it is supposed to be.
Just to put a slightly different twist on things, what sort of PROOF should be required that an animal has been misrepresented? I can point to several people who have received incorrect complaints of females being males - in some cases, the customers also mentioned that they paid too much for the snake, and they have found others for significantly less. While it may not nullify the complaint, it certainly raises some red flags for me. Short of video proof which clearly shows that it is the same animal, followed by eversion of hemipenes, we are pretty much forced to accept the word of our customers...and doing so costs us money in the form of return shipping, and/or another shipped animal.