One Ebay seller advertised a "fixed" S&H charge of $9.00, but then after
getting my money said it was actually $22 and change.

I should have asked for my money back, but instead paid an extra $14, only to
find the total shipping was $18. Would have been worth the extra $4, but so
poorly packed that item sustained scuffing damage.

I went to file a negative feedback, only to find he'd given me a negative for
REFUSING to pay for shipping. My feedback to him looked like "revenge"
negative.

You just can't win if someone is out to gouge you.

But to answer your question, I bid price+shipping cost, and if the combo price
is high, I pull back.