I've bought from ArtFire before and I love it! I've never had any problems from any of the sellers, I've bought different things from craft supplies to iPhone cases. Sure you need to be smart about who you buy from (just like any other site); scammers can be found everywhere online (even from the most reputable/professional sites).
It's part of our responsibility as online consumers to be weary & ask questions BEFORE buying anything. Be a smart consumer!