I'm all for the idea..as I've mentioned in the past, at almost every opportunity

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For too long, The idea of D.J's teaching and training other potential D.J's, was laughed at, and viewed with some professional Jealousy!. After all, the trainees of today, quickly become the competition of tomorrow, right?.
Wrong!, I've trained many people over the years, some have moved on and started up on their own, others still help me out today. True to some of them, it was purely a hobby which they have moved on from now, due to marriage / other interest's, but for about 5 at least, they continue to operate in the same town as me today, and I can never say, that to my knowledge any of them have either taken work away from me, or undercut me. I know for certain that at least one of them has recently declined to quote, when the client actually mentioned that they had already approached me before calling him for a "better" price. That's loyalty for you.
If you choose your "roadie" / Trainee carefully, you should be able to avoid the Ego driven, blood sucking vultures who just want to earn a fast few £££'s learn who your clients are, then disappear with your hard earned knowledge, and bookings.
I've mentioned before, that for most people who do eventually move on and start up themselves, provided that you have treated them fairly, then there is an unwritten code / respect that only a fool

where he eats, and there is enough work for everybody!.
Another advantage is that you have somebody local and trustworthy to pass work on to and cover for holidays / sickness etc. "How do I know he's good madam?"...."I trained him myself for 2 years".
Still view the trainees with suspicion???. well 12 months ago, who would have thought that you would be helping / sharing idea's with other D.J's on a public forum??.