I think if you post quality content on reputable sites, then you don’t have anything to worry about. I think it’s also ok to post on newer sites, as long as they are doing the right things and have quality standards.
Google is a machine (mostly) and can’t algorithmically differentiate between a guest post and a regular post (not all guest posts have the words “guest post” in it and regular posts often link out to other sites). But sites that accept low quality guest posts will be linking out to a lot of low quality sites – I think that will be the giveaway.