I don't think your honesty and integrity as a trainer are bent by the profession you come from, though they may have a bearing on the profession you choose.
I have to say that in my experience some of the best trainers (and the most honest) are those with “real-world” experience outside of their training experience. Seasoned practitioners, subject matter experts, or those who have recently completed their own training, are often very astute, very learner-aware, very passionate, and very attuned to the context of their teaching.
I have spent twenty five years in training and development (in one way or another), but I am a marketing professional and always will be. I got into training largely I think by accident, out of a passion for the relevant subject matter and extreme irritation at the way it was a) taught by the training professionals and b) practiced by the practitioners. So I suspect there is lurking within this unassuming exterior a crusading evangelist somewhat obsessed with impacting actual real-world performance.
I first put on a trainer's hat while I was still an idealistic business student -- as head of AIESEC South Africa, I had a mission to improve the relevance and quality of business education in universities throughout the region. When I started a real job as a market research analyst/consultant with A.C. Nielsen, I found myself teaching my peers how to do a more valuable job for their clients, which led to me teaching analytical marketing to Nielsen clients like Unilever and Revlon, which led me to become education director for the South African Market Research Association and to found and run an industry certification program.. At the same time, my passion for doing my job -- sales and customer service -- got me into teaching my colleagues basic skills such as presentations, sales, and consulting. Some major OD work resulted from that, which got me transferred to running Nielsen's international management services center to replicate the work world-wide. Since then I have run my own training/consulting/OD businesses in various parts of the world, focusing mainly on sales, marketing, and technology.
All of which background poses the question: am I a trainer or a consultant? Or am I a salesperson, or a marketer, or a researcher, or an entrepreneur? And does it matter? I believe I approach my work with a level of customer- focus, diligence and integrity that is unusual among “training vendors” and my clients would agree. I think I was born and raised to be that way. But, if my lifetime in consultative selling has influenced me, it has amplified – not diminished – my integrity.