What can you do to offset Yelp and their "review filtering?" I've seen many real reviews get filtered out by Yelp and it's frustrating!

We agree. Unlike Google who encourages businesses to ask customers for reviews, Yelp discourages it.
They want customers to organically/naturally leave reviews about a business and can suppress reviews if their algorithm thinks that the review was left because the business asked a person to leave it. Additionally, Yelp gives more credibility to reviews that are left by visitors who frequently review a variety of businesses on Yelp. (i.e. “Yelpers.”)

If you’d like a customer to leave a review on Yelp, first ask them, “Do you use Yelp?” If they say, “Yes,” then chances are their review will be viewed by Yelp as a legitimate one. Additionally, if a business gets too many reviews in a short period of time (i.e. a business has no Yelp reviews and suddenly has five reviews submitted), Yelp’s algorithm will flag them as being suspicious.

We know it can be frustrating, and out of all the review sites, Yelp is probably the pickiest, and you should think about your Yelp review strategy ahead of time.