This issue and thread is pretty cloudy. Im not sure what you are trying to get in this thread since you put an example of yakuza attempted a double spend on your site and thus this thread was placed on scam accusation.

However no proof / data is presented about this and it appears you are more into looking for a suggestion on how this issue wont be repeated in the future ( if this is so then this thread should not be in scam accusation )
If truly yakuza attempted a double spend on your site then you should present the proof to back what you claimed ( this is a form of scamming as well since he supposed to lose the 71.38 BTC )