Most equine places I have been to/looked into have required me to have my own insurance, as since they aren't paying me a salary I am not staff and therefore not covered under their insurance. I don't think that is that unusual.
As for why he isn't booked up-I agree, don't read too much into it. I've been to places that have waiting lists and I wouldn't go back, and I've been to places that were able to take me right away and I'd go again in a heartbeat. There are loads of reasons a place may not be booked up. If you are that concerned, maybe see about doing a trial day or ask around for what others are saying. Good that you are aware of your own safety, but at the end of the day you have to look after yourself so if you think something will put you in danger/get you injured-just don't do it.
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