There are no 100% guarantee. We just guarantee that you'll receive another not linked with you coins.
But if you use custom fee, time delay and several output addresses - there are many many chances to be untraceable. Usually attacker doesn't know that you use our service (unlike others).
Please don't forget to download and verify Letter of Guarantee BEFORE send us coins. Don't use TOR with our clearnet address.
So, you get my coins to newly generated address #1 and send other coins to me from other address #2 (this address alresdy has coins). Latter some guy sent his coins to your newly generated address #3 and you sent him my old coins from address #1. Is that correct or you have more complicated method?