I have to say I have some reservations about some of the options put forth here.
The seller has obviously made a mistake in both cases, and something should be done if possible to rectify it, but what lengths are to be reasonably expected?
First the time frame is pretty long. Errors in sexing are an unfortunate, but all too common occurance these days. In my opinion you should verify the sex of animals you buy, mainly to avoid such long terms in discovering the problem. It isn't like verifying the health of a snake, the health can change in 8 months, but the sex cannot.
Whether you verify it upon receipt or 6 months later doesn't change the fact that the seller made a mistake, but the length of time it took you to discover the problem factors into some of the options you are suggesting.
Concerning the ball,
1) Refund the different market value for the python at the current weight, and I keep the male, which was supposed to be female.
2) Replace a het female at approx. 800 to 1000 grams for the supposed to be female het (since my other female bought at the same time from the same person has grown to 1000 grams in the same condition)
Option one is affected by the length of time involved. Frankly I can't see this one happening at all.
Option 2 is the best case senario, and to me it would either be this one or a refund of the original purchase price.
On the boa
1) I will ship him back at the seller expense for a refund of the original purchase price plus the feeding cost I have spent from time of purchase.
2) Seller replaces a female at the same size and quality (if not better), and seller pays for all shipping cost involved.
3) Seller refunds the different in market price between a 5 feet male and female Peruvian. I still haven't figured out the different in market price for Peruvian, because it is based on not just size, but quality of the boa.
Again option one isn't going to happen. Feeding costs just cannot be considered in a refund. They increased with the length of time you have had the snake, and you cannot expect to punish the seller for that. Had the snake been the correct sex, you would have had the same investment in food anyway.
Option 2 is realistic, if the seller has an acceptable female.
Option 3 would be difficult because individual opinions of market value are significantly different.
Again replacement or refund of the original purchase price plus shipping fees are the only things to be reasonably expected.
While the mistake was at the hands of the seller, this is without question, at some point the buyer has to assume a degree of responsibility. This will involve the realization that feeding costs are not going to be refunded, and growth of the animal is another consequence of taking so long to report the problem.
As an example, my son bought his first snake, a female pastel motley cornsnake. It was a yearling at the time of purchase.
I never bothered to sex it, just trusted the seller's abilities.
Two years later I bought him a male to go with her and we discovered his was also a male.
Should I have went back to the seller and asked for a refund plus two years worth of mice I had fed the missexed animal? No.
Should I have even expected any monetary compensation after two years? In my opinion, no.
It was my fault for waiting two years to sex it, I should have done it immediately.
You waited 7 or 8 months, and in this instance I waited two years. Is there a difference? Where would the line be drawn?
What it boils down to is these are situations that we deal with as reptile keepers. It cannot really be compared to an unhealthy animal, it falls in the realm of human error, and we all make mistakes eventually. This should be taken into consideration when seeking a solution from the person who made the mistake.