The 3rd party acting as broker makes it a sticky situation. Can you 100% back up an animal that has not been in your possession since before it even hatched? Is the responsibility yours or theirs, or is it shared? Who's TOS do you follow? What is your terms of service? Who chooses when an animal is ready to be sold and what guidelines are you following?
Do you have any pictures of this "well enough to be rehomed" snake so we can get an idea of its overall build and what possibly possessed this person to think assist feeding was a valid option? Saying she had several meals on her own alludes to her originally requiring assistance. If this is true, how many times was she assist fed and how many consecutive meals did she take on her own before she was sold?