Lesson learned to always double check sex right away. I've received missexed snakes that I didn't check until years later (that's when I learned my lesson!). I've sold a missexed snake that the buyer didn't realize until years later. We're human, mistakes can happen and sometimes they are intentional but not always.
Is the seller 100% responsible? yes but it's also debatable to what extent depending on their TOS, the time frame involved and/or what the buyer expects as compensation.
Always double check sex (or have someone do it for you) so these errors can be caught quickly and it's more likely it can be resolved to the satisfaction of both parties. After 5 months, at least the guy was willing to offer you something.
Just my opinion.
