Just recently, we had our first issue with 2checkout.
We had a few (approx 6 apparently fraudulant orders).
These orders were suspect to us at first, and we had done our initial checks. Then 2co flagged them for review.
After about 24 hours, we received confirmations from 2co on those orders, which said that the transactions passed the fraud reviews, and we can go ahead and proceed with filling the orders.
Now, a month later, all 6 of those orders had chargebacks initiated on them. 2CO refunded all of them, and charged us a $39 fee for each one.
We have yet to hear back from them in regard to the matter, when we questioned their fraud review techniques, as well as their purpose for the deduction of the reserve fee, that was apprently for issues like this (but was not used in our case).
Again however, this is the first time we have had a problem with them. I just feel it's an important enough problem to bring out into the open.