What're the benefits of checking electronics in person over the exclusive online stores?
Don't the places you're shopping have a return policy for DOA or anything?  If they don't I certainly wouldn't buy from them if you think there's a high chance of a lemon.  So several questions:

1) What's the realistic chance of a lemon?  I don't know what you're buying, but I almost never worry about lemons when I'm buying things.

2) Will you actually be able to test the components to check for lemony badness while you're there? Do you have a realistic method of doing this and how much effort is it?

3) Can you even be sure you'll be able to get them when you're in China?  I'd take a sure thing over a chance, but if you have time you might as well look.  Which brings me to...

4) Can afford to wait?  I prefer having things now as opposed to later, and if you can't get it in China while you're there you're probably looking at a delay of at least a week ordering online thereafter.