Thank you for the links! I find this video quite useful too, since you can see the shape of the speaker's mouth.

I do find it easier to understand when people include the tone marks on the pinyin (though easiest of all is when they use the characters). I talked to a friend about this a while back in the context of leaving out the accents when writing Swedish, and she said a native speaker will understand it, but it's harder for a beginner — I hadn't thought of it that way before, but it makes a lot more sense to me now I've started learning Mandarin.

I would actually consider RP (received pronunciation/Queen's English) to be an accent in itself rather than a standard — the idea of it being "standard English" is a bit old-fashioned now, I think.

Thanks also for the correction re 蚵 — I will go and edit the posts now to fix it! I'm not sure where I got the idea that háo was correct.