Error refreshing iventory (querying prices of items). (response: 6:Error)

As Jerry suggested in his comment, you can work around this by calling

mHelper.queryInventoryAsync(false, mGotInventoryListener);

instead of

mHelper.queryInventoryAsync(mGotInventoryListener);

I have disabled all network connectivity from my device (for over a day) and can reliably reproduce/fix the issue with that single parameter change. Looks like the purchase itself will be cached for longer (indefinitely?) by the in-app billing service than the sku details like price.

It looks like Google Play has expiration of cached inventory items. That may be implementation detail of how Google Play app works.

Error 6 is defined as BILLING_RESPONSE_RESULT_ERROR.

If it's critical for you to offer inventory for purchase even without Internet connection, you may need to cache last returned results yourself, and use them in case that querying fails.

However, purchasing also would not work in such scenario, so why to bother?