I don't see why you should reconsider. You stated that you will remove the feedback once the issue is resolved and apparently they are delaying their response/refusing to respond.
I think this is appropriate in most cases, i.e., to leave a neg when a scam accusation thread is started by someone
and it appears to have enough evidence to support it. I wouldn't leave a neg simply because someone started a thread.
DT members in general are not consistent in tagging people based on scam accusation threads, and there are probably many reasons for that. OP, if you see one that hits home, feel free to tag someone even if no one else has. If you were in error, it will sort itself out eventually. The person who got tagged will most likely make a fuss, which will bring other DT members' attention on the situation and you'll get feedback. That's what's happened before in at least two cases that I can think of where I gave the only neg to someone.
It's also good that you're soliciting help from the community, and in time your confidence in your judgement will become stronger.
In this
particular case, it seems justifiable to me, and if the member's response to you wasn't convincing, you should keep the tag on him.