My thoughts in selling my own personal work are that it becomes the level of communication within these images that people enjoy - the technicalities of what camera, what lens, what processing or what printer are not so important to my clients.
Clients don't care what you are using, they simply want results, and nothing more.
These equipment discussions crop up frequently..the obvious answer is to use what you like (handling, ergonomics, personal taste, cost etc)
Whilst I only do some part time work, nobody has "ever" asked me what I use, what lens took a photo, etc etc. And they would not be impressed much if I told them ;-)
Saying that, there are obvious limitations to some cameras, nobody would out of choice take a fuji compact to a wedding, you could still get some decent shots, but you are making life hard.
I would go so far as to say, the only people who do ask about equipment, are photographers..most folks wouldn't have a clue about an L lens v a kit lens, or a cheap flashgun v a top end one.
You simply have a choice of makers, and equipment makes your life easier..there are 3 that have fairly complete systems, and other makers are worth a look too.
The same goes for landscape work, folks can talk mega pixels and res all day long, but it is the prints that tell the real story. The actual quality of the photo, not image quality. Technical flaws may not render an image sub standard, it can still be very good
It's even open to debate if you "need" a full frame camera, certainly for many jobs an APS one will be more than enough.
Just a note to Ray here, I shoot 6mp and 10mp alongside 35mm film. And I have questioned and being more specific, simply looked at the prints I have done. And I can say, without any hesitation, that neither of my digitals can "hold their own" up to a quality 35mm scan. So if people say 3mp does so well, I would have to strongly disagree, based on my own use of all of them. Not that I am unhappy with the digitals, simply I am satisfied with the output of good quality 35mm, some are not..some want larger formats..that is fine, choice as they say. But the reason I do use "some" film, is not for simply resolution, it is on a tonal and sometimes DR level, hence my gravitation to neg film, against the trends of most scenic shooters. I prefer to use digital for low light work, as it has a notable advantage over film. I really don't want to read any more of this "3mp near 35mm" it simply does not hold up.
If people want to talk about print sizes, my little comment above, had no impact. You cannot talk about that, unless you talk about viewing distances..from normal distances lower resolution prints will hold up just fine, only the print/pixel peepers will have a problem with them. There is nothing wrong with talking about res, to a point, but we hear so little about other areas, tonal variations, colour reproductions, hues, saturations, dynamic range..and various other ones.
You are either satisfied, or you are not (print wise)