Talk to people. Ask those who have been a WS who they would suggest. When you talk to the BNT, ask for specifics: what kind of hours are you putting in, what is the daily routine, how often are you able to ride, and, what is expected of you/the BNT? Communicate clearly, and ask questions about what is important to you - last thing you want to do is commit to months of what is essentially slave labor, and get very little out of it in terms of your goals.
The window of appropriate BNTs to work under gets narrower and narrower, the more you talk to the people who have actually been a WS for those said BNTs. Don’t listen to what other professionals who haven’t been in the BNTs’ program say - listen to what the WS’s past and present say. And some will say a lot.
I think being a WS is a wonderful way to advance your knowledge and riding skills even if riding professionally is not your goal. It was never my goal, either, and I worked for three BNT riders throughout my teens and early 20s. For me, being a WS was a chance to ride quality horseflesh I could never afford, and I got that opportunity in all three programs. Make sure if riding is your goal, that you find a BNT that will expect you to exercise ride their horses (many don’t!!) as part of your job, as well as provide lesson[s] to you a few times a week on your own personal horse if you have one.
Most WS positions do not offer a paycheck. Some might offer a stipend, but I have found the better WS gigs (as in = fair, honest, and a good value for the WS) usually will trade the WS’s labor for free room & board, and one or two lessons a week. I would go for that kind of deal any day over a stipend, because there is significantly more value for most people in having a place they can bring their horse and learn, vs being “paid” a pittance monthly.
There is a big failure and burnout rate in the industry for WS positions. Some of it is on the fault of the BNT, who expects way more than fair labor – but some of it is at the fault of the WS – who finds out too late, that they do not want to work so hard for what is essentially the most laborious job they’ll ever have in their life.
My advice would be to do your homework – thoroughly. Talk to people that have worked under the BNT.
I have had many jobs, and several career paths. I have worked hard my entire live, and still, have never worked so hard in my life as I did as a WS.