feedback on non-payers

Look I'm new to this. BUT  I've had two experiences with people buying and then not paying.  Not Auction situations.

One I referred to the Resolution Centre & was eventually paid.  The other, I just cancelled the transaction.  Both are sitting there waiting for my feedback. 

I feel that I need to leave the negative feedback which is warranted, in order to alert other sellers. 

But on the other hand am concerned about the backlash. 

As i understand it, the buyer who who was dealt with by the Resoution Centre has no right of response. 

But what about the other Buyer - who I initated the cancellation?

As I say  - new here, don't want to cause grief, DO want to be responsible.  Please alert me to issues.

Thankyou for he previous guidance I've received here.  j