I suggest you take a look at this a16z resource first (it’s free). Then, take stock whether you’ll need the bootcamp. https://www.youtube.com/playlist?list=PLM4u6XbiXf5rtyzi7g-5ObKubmZFiTIlD
There's also this book: https://www.linkedin.com/in/buy-thesalesenablementplaybook/
The reason there is such varying quality is that “sales” is such a broad topic. You could be signing up for a bootcamp for people selling anything. The processes for selling b2b technology tools are drastically different than, say, selling insurance and financial products. Make sure you are in an appropriate course, given your market, your team composition, your product stage, etc.
With that said, here are a few people:
https://salesbootcamp.com/ This is a bootcamp from James Nielsen (mentor at Alchemist). Its focussed on training SDRs but might have something for founders as well.
Alchemist mentor Kevin Ramani offers sales process bootstrapping services for super early stage startups. You learn a lot during the course of the engagement. I recommend at least a conversation with Kevin.
Mike Duchen, another Alchemist mentor runs a bootcamp style workshop for founders called Inside Sales Bootcamp.
Here's (https://docs.google.com/document/d/1ZHCSm5yUAGhdpDH9VFTPS271LZ-RgF3YHkvZQePxGnM/) a preliminary copy of an awesome book. He has had major success selling as a founder including successful exit (his credentials are in the book itself). Its a very good jump start if you are “read the book and implement” kind of a person.