So I had 197 legendary marks... I played a few rounds of Crimson Doubles, then a round of Control (the daily) and got only 3. Okay That's normal. I went the Reef to pick up Imogen's Fire (which doesn't cost marks), went to the Exotics kiosk for two guns (which also doesn't cost marks)... Switched characters and went to Shaxx for my crimson doubles quest, and then I broke down a few legendary weapons because I forgot I had a full stash... When I remembered (immediately after the second gun)... I checked and found that I only had 60 Marks left? (Which then reminded me that when I was at Shaxx, all the items were blacked out - I didn't have the requirements to buy them.) I really can't think of any way I could have used the marks (didn't go to any of the other vendors).