So you just learn by lots of practice.
That's NOT what I said, is it? Sure, lots of practice is necessary but is not enough on it's own, there's simply too much to learn for anyone to become particularly good just by practice/trail and error. As Alcove has said both here and previously and I said in my last message and previously, it's essential to observe and be taught by an experienced, successful practitioner. Again, please read and try to understand what we are writing!
Well if I want to hire someone for my next project, what should I look for then?
I've already told you but you don't seem willing or able to put 2 and 2 together and understand what you've been told! The art of mixing is primarily defined by what you hear and what you hear is defined by the sound system/room acoustics. The type of mix you want will dictate the sound system/acoustics required and therefore define what the mixer hears and ultimately how they mix. For example, there is no stereo (2 channel) theatrical audio format, so if a film festival accepts stereo mixes for screening the chances are they (and the filmmakers being exhibited) don't know what they are doing and therefore any decent stereo sound system/acoustics is just as likely to be appropriate for mixing as any other. 5.1 is however a theatrical format and cinemas install very specific theatrical 5.1 sound systems, in very specific acoustics and all of it is very specifically calibrated. In order for the mixer to mix appropriately, they have to hear appropriately and that means mixing in a theatrical mix stage (which obviously has the same specific 5.1 theatrical sound system, acoustics and calibration)! A theatrical 5.1 mix is therefore massively more expensive than a TV (HDTV/DVD/BluRay) 5.1 mix, which in turn is more expensive than a stereo mix.
What you need to "look for" as a basic first step is a combination of: 1. The correct facilities (mix room) for the type/s of mix you require, 2. A Re-recording Mixer who has the skill/knowledge/experience to use those facilities and 3. An appropriate amount of time to allow the Re-recording Mixer to do a decent/good job.
This also feeds back into your incorrect statement that one learns "just by practice", practice on what; a stereo system, a TV 5.1 system or a theatrical 5.1 system?
Not LEARNT, it's LEARNED.
Actually it is LEARNT! "Learn" is an irregular verb like "burn". "Learned" (pronounced learn-ned) is an adjective to describe someone who is very well informed/educated on a partiicular subject. I realise in the US that "learned" as an adjective has been dropped and it's now used by Americans as just the past tense of the verb "to learn" but that is technically incorrect or maybe it's been done for so long in the US that it's now considered to be correct there but in the English language "learnt" is the correct past tense of "Learn".
Personally, I figure out what the level of the short is and then work out how much I went to spend.
This is a bit backwards but the basic philosophy is good. There's obviously no logic to spending a large sum of money to have a commercial quality sound mix made if the rest of the film doesn't match-up to that level of quality. Most commonly though the situation is the opposite way around, a disproportionate amount of time, effort and money have been put into the visuals and the sound mix detracts from the film rather than adds to it. The key is finding an appropriate balance, which was I think your basic point and one I would whole-heartedly agree with.
This meant my decision was to do the mix myself and pay a pro to do a quick 8 hours (for an 8 minute short) to bring it into line with a stereo mix for cinema.
Baring in mind that there is no such thing as a "stereo mix for cinema", paying a "pro" to bring your mix "into line" with one is a pretty vague target! Certainly paying a pro for a few hours should substantially improve the quality of your stereo mix though and hopefully achieve at least roughly ballpark levels.
G