Sort by rating

I'm curious how googles algorithm are working when it comes to sort by rating, it doesn't make any sence to me as looking at the 3-pack the listings there have less rating then a client of mine that have 4,9stars, my client is at #6 he have 60 legit google reviews/ratings with a total of 4,9stars and he have around 100fb rating/reviews same thing there average 4,8. There is one listing in the pack that have 4,2 in rating and 22 google reviews and even less fb reviews with lower rating. This doesn't make any sence to me so i wonder what really controls the sort by review listing?

Reviews have their own algorithm but Google does take the account of a bunch of businesses in the industry and area it then calculates how many reviews a business of that industry in that area should have so they take an average if most companies only have 22 reviews and you have 100 that could be hurting you because Google even if legit is going to say hey how do you have more than the competitors even if your just more engaged they see it as your asking for reviews which is a grey area. Personally looks like you may just have too many reviews vs competition they also look at the time span between each review are they all coming in weekly, monthly, yearly, daily etc.. the algorithm detects lots of things not always does having the most reviews hurt you but in lots of cases it can.