Park West is very litigious - but as David said, the cruise lines are letting the contracts expire.
The new Cunard Queen Elizabeth will not have Park West onboard. Oceania also dropped them a long time ago, and they are not on the new Celebrity Eclipse. I'm pretty sure Oasis and Allure don't have them either.
The only new ship to still have them is NCLs Norwegian Epic., which has the largest Park West Operation at sea yet - six salespeople. I was a little surprised when I saw that, but I magine they made a deal NCL could not refuse.
The reason they are still on is because it only takes a few suckers on every cruise for them to make huge amounts of money.
It is a shame - I will say that I do not think Park West is like a criminal organization - I have seen them refund money to people who are not satisfied, but really, in the long run when you look at the big picture - with them selling questionable prints at way-inflated values (based on what people find when they get home and try to re-sell the prints) - it is a fact that several people have spent over $50,000 in "art" and been told not soon later by people in the business that what they bought was essentially worthless.
There is no justification for that no matter how much the company makes for the cruise lines - it is a disgrace.