Let me add this. Whatever the price the DJ was to be paid, that DJ should have been more professional than that. The way he dressed was terrible and not having the right music for specific parts is no excuse.The bride's only shortcoming is that she didn't meet personally with the DJ or check references.
Otherwise I agree with the bride, and those of you who take issue with her need to do a better self assessment. This is particularly true for any of you who do everything online - as if that insulates you somehow from doing any real customer service.
The DJ solicited a detailed timeline and extensive list of music then didn't bother to bring his requisite instruction manual. WTF? $600 is more than enough to follow instructions and live up to commitments while dressing appropriately. This gig was a cake walk. It didn't have any unusual or extraordinary requirements, so the notion that the price in any way matters is totally lame.
I look at it this way. When at work you're providing entertainment for your client and their guests. You never know who may be in need of a DJ in the future or someone else they know. So you should present yourself as a true professional. Especially when doing a wedding or some other formal event. You never know what business you might get to fall in your lap because you acted and looked the part of a true professional.