At the end of every introduction to archery course there will be a few wanting to buy equipment straight away. In my experience, saying "Don't" rarely works. What they should really buy is a take down beginners' bow with which to develop the correct technique, but somehow they come back to the club with a sparkly new bow that the archery shop has persuaded them matches their favourite jumper.
For the moment I will just repeat what I said on Facebook:
WARNING FOR NEW MEMBERS - before you buy any equipment you need to know your draw length, the length of bow suitable for you and the poundage of the bow suitable to your experience. You also need to know whether your eye dominance has been correctly determined and handedness has settled down - may take weeks after finishing the course. Once you know this, then you can go and buy that nice yellow bow with red go-faster stripes.
If you have any doubts about the accurate measurement of an archer's draw length, the range of bow lengths suitable for the range of draw lengths, the poundage range suitable to the individual beginner - then refrain from giving advice.
If you want to improve your ability in giving advice to beginners on equipment purchase, have a look at www.learn-archery.com/proper-bow-size.html which runs through the basic steps in selecting the correct bow.