Most importantly, their privacy policy should be easily viewable on the site so that you yourself can see exactly how they use your data.
http://forum3.bandingklub.cz/viewtopic.php?f=14&t=1368684
https://45.83.123.20/viewtopic.php?t=14046
https://ufr-2020.front5.picapo.net/forums/viewtopic.php?pid=375611
http://bbsc.gaoxiaobbs.cn/forum.php?mod=viewthread&tid=50171&extra=
http://www.suseage.com/forum.php?mod=viewthread&tid=880096&extra=
https://www.ww2.site/forum/viewtopic.php?t=78586
http://47.88.101.141/forum.php?mod=viewthread&tid=137016&extra=
http://forum.bandingklub.cz/viewtopic.php?f=39&t=1166079
http://www.lada-xray.net/showthread.php?p=143133#post143133
https://forum.zweb-apps.xyz/viewtopic.php?t=24078
https://debate.socialism.nl/forum/showthread.php?tid=170432