Prices say "Free"

Check your financial delimiter setting. You should use . in an amount. Like the cost of a product is 9.99

Just for the record.

I had this problem and solved it myself. I was exporting from a price list that had the currency simbol “$” and once I erased it from the CSV file I tried importing again and after so the price was merged and updated with no problem.

I hope it could be useful for you.

yes, please use . and no sign in front. Also check out this https://allaerd.org/delete-products-import-woocommerce/.