Exactly. If you get 50% feedbacks back you're doing ok. The only way to get more feedback is probably to have a message go out to them requesting feedback for the awesome service you provided. This may help get a few more feedback responses, but the fact remains, some buyers won't leave feedback regardless.
However, with the 4.3 DSR rating on one of your DSR categories, that's not good at all. I would suspect they will drop you to a 'Below Standard' if you're not there already. After that its just a matter of time before they kill you off with the dreaded 'Indefinite Restriction' email notice.
I would quickly try to fix that category, even bending over backwards otherwise you'll get shafted by ebay.
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