Proxies are merely middlemen for other shops, so you couldn't say for a proxy "no you will definitely not get a bootleg" or "yes you will". I'd say it might be more appropriate to make lists for individual sites (e.g. Amazon JP). Most stores have a shop thread which can be used to check a store's legitimacy.
Otsukai is people reselling you stuff (normally off of places like Mercari), so you'll have to do your own due diligence there, best you can. Not sure how strict they are with booting people who try to sell bootlegs - but they do say to contact support if you have suspicions of a bootleg.