In fact liver only directs toxins to other parts of the body, most notably adipose deposits (fat). The liver itself does not accumulate toxins. I only eat grass fed meat and offal, and I am convinced that a high fat diet is best for the human body, but if you want to stay away from toxins in store meat, the best strategy is to buy lean cuts, which may include liver. Of course it is only a partial solution since fat is one of the two main reasons why we eat meat in the first place (and lean meat is also poor in collagen...).
Liver, at least, has nutrition far exceeding muscle, including vitamin A and B12 which are an issue for a large fraction of the population. I eat it once a week for prevention.