Scratches and scuffs... it does sound like you got a 'pre-loved' unit. Nothing to worry though, those things are bullet proof almost. The one I have (no longer on the bike though) I bought from a guy in Canada and it served me really well for over a year... only removed it to put another used unit in it. This time I went with the Kawasaki Race ECU and etc...
The Race ECU also came pre-loaded with a map and even after I zero'ed it, it still wouldn't work how it should and the bike had maybe
80hp. It wasn't until I had the bike dyno tuned properly that it worked. It had me thinking I had messed up on the install (same as you) and I re-did everything at least 3 times... and that's replacing the whole harness 3 times!!!! Massive PITA.
Check the video bellow... this is the bike before I had it dyno tuned.
You can check on my other videos and compare the speed at the end of the straight but if you're as lazy as I am, you'll be happy that I told you it used to cut on 6th gear for like half sec with the Bazzaz on and saved you having to watch someone else's videos.