I had a situation where a company got into the company I was running at the time for about $60k, they were about 6 months behind on this bill and I was responsible for letting get that far (long story). We were holding about $500k of inventory they supplied us to make our assemblies. At their next order their inventory went missing, we couldn't find it. They got ****ed, told me I was holding their inventory hostage, these items had about a 6 month delivery. I assured them I would never do that and that we had just misplaced it, I was sure it was safe, but I really didn't feel inclined to look for it until they settled their account. It took them about 2 weeks to realize I was serious and their parts still hadn't shown up. Finally they settled the bill and asked when their order would be filled, I told them they were COD, which they paid. Then they asked for their parts, which we had found and gladly gave to them.
I left the company about a month later, one of the guys at the company I left, I guess didn't like me, ranted about how I had cost this account, which was probably worth about $100k a year but had huge potential (roll eyes), they refused to buy from us again. About six months later this customer declared bankruptcy and screwed people out of millions of dollars. I chuckled about the ranting guy and felt bad for the people who got screwed.
My point, holding stuff works to get paid, there are people who are masters at screwing others out of payment for services supplied, and generally there is not much you can do about it.