Sales rep is the only contact
No technical engineer, no senior delivery lead, no past-customer reference. If the only person you ever talk to is a BDR, you are buying air.
Generic demo, not yours
A polished demo built for a different industry is not proof for your industry. Ask for a live demo of a customer in your category before paying.
Slides-only sales pitch
No working example, only slides and architecture diagrams. The product does not exist yet; you are funding R&D.
Open-ended scope and budget
Open-ended timeline plus monthly retainer plus six-figure budget plus no milestone payments is a classic burn pattern.
Refusal to negotiate IP
If the vendor refuses to negotiate IP ownership or model disclosure clauses, walk away. The contract is the only leverage you have post-signing.