John,
for the camera not working, it is exactly the same. Think for a minute. You buy a camera and NEVER check to see if it works. You leave it in the box on a shelf for 8 months. When you decide now 8 months later to try the camera out, you find out it doesn't work, and probably NEVER worked(it sat on a shelf for 2 years with no interaction from you, so you didn't drop it or break an attachment, it was the exact same as when you bought it). Now, what does common sense tell you when you buy a camera or some other electronic gadget? Plug the darn thing in when you get it to make sure it works!!! You wouldn't leave your new camera on the shelf for 8 months, you would have popped batteries in it and tried it out as soon as you got it, right? The seller told you it worked, so you are going to assume it works and never test it out to see? That is a firm NO I can pretty much guarantee it.
This is the same with the snake. You paid for a female ball python. The seller popped it in front of you, okay. What if the seller did it wrong? What if the snake didn't want to be popped and tensed those muscles up? You just believed him on what is generally known as not an always accurate sex determination "trick(couldn't think of a better word)" and you were too lazy/squeamish/busy/lazy to get a second opinion. Like with the camera, common sense would at least tell ME to probe it myself(oh wait, you refuse to learn how, so scratch that) or at the VERY least get it to someone who CAN and WILL just to be sure, ESPECIALLY if you're spending the kind of money you're talking about in het animals(oh wait the place that checks for you is 45 minutes away, and you're too lazy/busy/lazy to take the snake there for firm confirmation). Basically, you left the snakes in the cage for 8 months before bothering to check if they were the correct sex. That is essentially the same as leaving the camera on the shelf for 8 months before checking if it worked. Both were problems/mistakes that existed on the seller's side from the beginning, noone doubts that. However, it was YOUR mistake to wait so long to verify that a mistake was ever made.
I think it's a perfectly good analogy(but of course, I made it up, so I guess I WOULD like it, eh?

).
Now, I am glad that the seller of the ball python was great. He went above and beyond in customer service, and if you wouldn't mind, I'd like to know his name as he sounds like someone I would like to buy from. Heck, ANYONE that would take my word for it that they missexed a snake I purchased 8 months ago and immediately give me two free females to make up for it is someone we ALL need to do business with. This is no offense meant towards him, but I bet the scammers would love him. "Hey, I bought a female het albino from you a year ago, and uh, now it's probing male, can you give me two free females like you did that other guy to fix this?"
Now, would I go out and be THAT customer friendly to you 8 months later? Honestly, the answer is NO. And here's why(I'll explain it again)...
After 8 months of food and growth, how exactly am I too be sure it is the snake I sold you in the first place? Most snakes(even ball pythons) can look pretty different after 8 months of growth. What kind of care has the snake received? Does it have mites, respiratory infection, blisters, etc.? Has it been exposed to something that I don't want coming into my collection if I take the snake back? How exactly am I too be sure it is the snake I sold you in the first place(yes, I know I'm repeating myself)?
And yes, I WILL fix a mistake I made. Call me up within a few days of the sale and I can happily replace or refund the animal with the proper sex. Heck, like I said, 8 days or 8 weeks and I'll likely be happy to do something about fixing what I did wrong(the snake shouldn't have changed or grown so much in that time frame that I wouldn't recognise it). But call me up 8 months later when I have no way of verifying it was the snake I even sold you in the first place(chances are also pretty good I won't have pics on file or feed charts or anything like that anymore since the sale was concluded 8 MONTHS ago). Plus, if you told me when you got the snakes that you were happy with them and they arrived okay, it's kind of hard to wonder why all of a sudden 8 months later you're wanting a refund/replacement plus a higher value animal and money for feeding expenses, and it would be VERY hard for me to tell you anything but where to take it.
Like I said, sorry you won't do business with me because I would refuse to take it up the a$$ because you decided 8 months later to verify the sex on snakes I sold you. If you could prove to me those were the snakes I sold you, I'd admit to it, and MAYBE(big maybe)even refund your purchase price(though I'm not giving you $500 because that is the "current" value, you didn't pay for a sub-adult, you paid for a hatchling and that is what you'd get refunded for, if at all).
It's hard to make the customer happy further down the line if they had a problem they never bothered to tell you about.