不少家長認為，孩子在學琴初期，只要隨便找個老師就行了。等練到四五級以上，再去請專業性較強、水平較高的老師來輔導？

This sort of thing could only happen in Hong Kong. This mentality, "一般取得英國皇家音樂學院入學資格（即八級）都可以教的。當然考獲教師文憑就更好" is seriously, seriously flawed. It is like saying: "every primary school graduate can teach primary school. If he graduated from secondary school, it'd be better". Doesn't make sense, does it?
Qualification has little to do with the actual skill of a musician - there are tons of Grade 8 graduates here in Hong Kong, but how many could actually play you a proper Grade 8 piece? I meet Diploma students here who are just about the level of Grade 6 or 7, who have absolutely no knowledge about music (just see how many people here on Yahoo asking for help on programme notes - if you are at Diploma level you should be able to do some of the programme notes yourself!!!). Hence, the actual skill is something more than just a qualification. It is an ability, not a qualification. If you said you're a musician, play me a concert - preferably with accompanying programme notes written by you - and I am convinced. Anything less, you are just faking it.
After verifying the teacher's skill, one needs to realize that teaching is a separate matter. Teaching in itself is a skill, and it takes years of experience, keen observations, as well as a good understanding of psychology. A simple test for a young teacher is to see if she could write (not just verbally) her teaching philosophy. Again, one can easily fake her teaching abilities verbally, but to be able to write with considerable skill and coherrence is certainly a demonstration of her maturity and insigfulness. You want a teacher who is mature enough to be a mentor to your kid, not another playmate. The older teachers are usually better as teachers, but here in Hong Kong, not all of them are reliable too. It is so hard picking a teacher!
In cities like New York or London, this is not a problem at all. You can't fake being a musician, hence, even if you 隨便找個老師 he'd be someone somewhat reliable than 隨便 in Hong Kong 找個老師. None of those so-called teachers would survive in New York.
Please don't use Grades and Levels to judge an artist. It is so naïve. And don't use Grades and Levels to judge a student either, that is even more naïve.

so true

我有時覺得....學歷唔係最重要....而係,睇下個老師可唔可以令到d小朋友真正愛上彈琴,把上堂變成樂趣,如果唔係.....個小朋友就會唔中意,什至討厭學琴.....

你說隨便是怎樣隨便？專業又專業到怎樣呢？
一般取得英國皇家音樂學院入學資格（即八級）都可以教的。當然考獲教師文憑就更好。
一個好的鋼琴導師應該有音樂修養、如果教小朋更要有耐性、有愛心。
樂琴最好跟定一位老師，不要轉來轉去。八級後有興趣才找新老師再進修。