My seller ratings vanished even though i have many sales and far more than 10 feedbacks. The following response from Ebay sounds like this will happen every year.

Hello Ralph,

....

Detailed Seller Ratings ..refresh every 12 months.

Now, the Detailed Seller Ratings actually would refresh on a 12 month rolling period. Your account has just recently restarted. Based on the 12 month trending, your 12 month rolling period would start on the Month of August.

What you need to do is to count the Detailed Seller Ratings starting from August 2012. You can’t include the Detailed Seller Ratings on the previous months