You can view up to 10 reports a day for traffic on SEMrush, their data is pretty verbose, but again there is no way to get a 100% accurate number besides asking the domain owner themself!
You will not get accurate data. And if the site is not popular or takes some real traffic at least 1000+ visits daily than it will be even harder to get any information. If You wanna buy site just ask seller maybe he will be that kind to share .
If it is your own website then your hosting provider probably offers some kind of traffic report. In addition you can set up google analytics and start getting reports that way.