The vendor was talking a load of rubbish, having a transaction in the resolution center to extend the shipping time has absolutely zero impact on your buyer stats. When they said a refund is better I suspect they were referring to being better for them, not necessarily you because a refund on your buyer stats is def not better for you. At the end of the day it all depends on what you want more, personally I try to avoid refunds at all costs as a high refund rate will def cause you issues.