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Well, this is the problem with hydraulic and air sprung kit (and why buying it used is always a matter of trust) - the extent of some issues do not come to light or are apparent immediately. If the brakes were still borked after 10 hours and it was apparent that the fork was not working properly in that time scale or there abouts then the seller has questions to answer. 20 hours? Maybe....depends how the kit was sold “perfect” vs. “Used”. 50 hours? Not so much.
Did you tell them that it all worked properly? Or that you looked after it? If so then you should try and sort it.
If you told them something like “no idea if it all works, sold as seen” then yeah you can probably walk away.
Most people expect stuff to work and not be fucked - unless warned otherwise.
If this was eBay and the item wasn’t sold as spares or repair you’d probably have to accept a return.