Let's continue the discussion...
Portfolio.
If I was to get a call from a client and asked for extensive portfolio, I would have nothing to show for. I'm a freelancer mainly for two studios. All the wedding stuff I do, stays in the studio, most of the gear that I take on the job is also studio's. So if I am being judged, I'd have
nothing to show for.
Photographer that shot my wedding, I assisted the guy till his last job, (few months after which he passed away

) he was a freelancer for about 5-6 studios regularly and he him self had no portfolio to show of if asked.
So, as important as it is to look at someone's work, personally, it isn't the first thing I look at but rather engage in a discussion of photography and background, etc etc.
Favor.
We all done it. My wedding was shot for free, may he R.I.P., the only thing it cost me was expenses - assistant's salary and printing proofs. Albums I did separately so that was a different price quote.
Knowledge.
Contrary to few PMs I got and to number of rebukes I got, I'm just a 29y/o punk. I've only been in this industry on photo end of it for 10yrs. But I was lucky enough to learn first and foremost lighting. Try shooting a wedding indoors with a 220 film and no light source or only ambient light = wide open lens, slow shutter -> will look nice on portraits
if done right but everything else will look like crap. Only after getting a hand on lighting, I got to play with actual 6x6 bronica box and even that wasn't as simple as it seems. #1, you only got 24frames on your roll, so you have to have second back ready to go. #2, loading and unloading film is EXTREMELY important, otherwise you'll loose EVERYTHING, it isn't like a 35mm chamber. #3 got to frame and compose your shots with printing format in mind (4x5, 4x6, 5x7, etc).
Wedding is a once in a life-time event,
hopefully. And should be captured by someone who is specializing in it. There's nothing wrong to shoot it as a favor but there's something wrong if one is mainly shooting landscapes to shoot a wedding. I'm a wedding freak and the other day posted some jewelry attempts for CC and got my @$$ kicked on it. I'm glad it happened b/c its a way to learn but that's before I sign the contract/ accepted an assignment to shoot jewelry.
So knowledge and background, by far in my opinion is more important then portfolio and one can easily spot this by asking few technical questions that every photographer, especially wedding photographer knows.
I don't mean formulas, b/c I hate them my self.
EDIT: After I wrote my essay, I saw this
That is actually how I got started shooting weddings. Both my nieces got married in the same summer and they insisted I shoot their weddings.
The difference is I already had 5 years experience with nature photography and knew how to process photos so was able to turn out good photos....just wasn't used to working with people.
I did my first 6 weddings for free until I felt I was good enough to charge...then slowly raised my prices as my work improved.
Shockey, you said it, you already had experience with photography. You already know that dragging shutter to 1/10sec w/o a tripod will LIKELY, produce blur effects or that shooting the whole wedding at 2.8 will mean soft images. Many folks, however, and I think that's where OP comes from, end up buying 2.8 lenses, shooting the whole job then coming on forums "what did I do wrong, why are my images out of focus, why aren't they sharp" meanwhile, client's memories are crappy while they did spend $ b/c he/she has to pay off the 2.8 glass. On another forum, I was replying to Q where a lady was trying to shoot a portrait with a 50 at 1.4 and couldn't figure out why standing 7-10 feet from her kids one in the middle was relatively sharp why her ears as well as sisters on L & R were blur. She later came back saying that clients are suing her and again she can't figure out why.