That's all very interesting (am author myself, BTW).
I think it might be hard to coach on, say, getting through writers block if you don't come at it from a writing point of view. SOmetimes it happens for quite specific, technical, reasons (the premise isn't clear enough, the character don't have enough at stake, or enough opposition, the story is being told from the wrong POV, or starting at the wrong place, etc), though your short story writing experience would help.
As far as the selling part is concerned, for lots of writers approaching publishers and/or agents, that comes down to being able to write a good query letter. Again, query letters are a very niche area--I worked in marketing and PR for 15 years but still had to do a lot of learning about how to write them when I started pitching to agents.
And when it comes to selling yourself as a published author, again that can be to do with knowing how to get the ever-increasingly-important blogs to review your book, how to approach booksellers, etc. With the exception of the latter, a lot of this isn't done in person. When it comes to actually talking at festivals and signings it certainly does help to have some self-confidence (or an appearance of it).
WHere I think someone like you could score would be with the bigger questions of what people are trying to achieve with their writing: to be published or to express their creativity or to finish a family history book or memoir. Or just to do something for themselves that isn't work or looking after children/family and carving out time for it.
I'm just thinking aloud here! The trouble is that a lot of published authors are in big trouble financially now. Money is really tight. On the other hand, people who are writing as a side-line and already have another job to fund them, might have the cash to buy in more services that aren't writing-specific. At the moment, the only thing I'd want to spend any more money on would be a first-rate book PR, in the hope of kick-starting my next book when it comes out! On the other hand, I might value someone kicking me into trying to find some more freelance editing work to help my cashflow.