@methyl,
I think mayennaise is asking how these people arrive at their valuation of their company, so as to know how much to ask for and how many percent equity to offer. (I would like to know about this myself!)
As I understand it, if they ask for too much of an investment they risk not being offered any kind of deal and have to "leave empty-handed". Over-valuing their business is where it all usually goes wrong.
What so often plays out, in recent series, is that the Dragons agree to meet the amount of cash requested but always ask for about double the percentage equity the visitors had in mind.