They tended to share a number of features.
1) great promises of future business if you helped them now. Business which not only never materialized, but later on as you learned from other sources, they never had any intent to work with you on.
2) eager to engage your team due to their recognized expertise in solving problems, and scoping out solutions. Again, usually with a promise of working together on an RFP, or a future contract. The reality was they wanted free consulting.
3) POCs on your kit, demonstrating your performance and cost superiority to other solutions, with again, promises of if the POC went well, they would purchase from you. They refused to sign a contract indicating this. And later the bought very expensive gear from a competitor (about 5x our price) which purportedly did the same thing (it didn't) at the same performance (it didn't). Later reaching out to us to ask us to help re-engineer their purchased solution (we didn't).
4) RFPs that you responded to, and according to the non-purchasing folks, you dominated and won. Later changed by the purchasing people. In one case, a university called me up on my vacation asking me to teach our competitors how to do what we did. Because they didn't want to buy our solution from us. But they wanted our solution.
Fire your bad customers. In the case of the university, we simply stopped responding them them after they pulled that crap. I'd get occasional complaints from them and others that they needed me to respond to RFPs so they could get their minimum of 3 offers to compare.
We had a non-US government purchasing entity literally change a contract on us because they could, and told us they could, without us agreeing to it.
Every single negative interaction wound up being represented in our T&Cs. After a while, some of the larger groups we dealt with complained about our T&Cs. Which weren't one sided, but they were fair to both parties. I am thankful that this provided signals of problematic customers. I'd sit down with the entities lawyers and explain every single clause and why it was there. I helped them understand what were lines what was non-negotiable.
Most reasonable entities adapted. The unreasonable ones would insist upon their own terms, which were tremendously risky for us.
Almost 4 years since the company was killed, and it's getting a bit easier to write and talk about this.