How do you vet investors to stop wasting time on free itemized estimates?

Hi everyone, I’m a contractor from Memphis TN who is investor friendly and I'm running into an issue with real estate investors asking for free, fully itemized estimates upfront. I end up doing a ton of footwork, driving out to properties, meeting tradesman, and spending hours writing detailed line-item scopes, only for the investor to ghost me or use my bid to negotiate a price drop with a seller. One investor dragged this process out all the way until (we'll be starting next week when I close on the property). I want to work with investors, but I need to protect my time.

• How do you vet investors before driving out to a property?
• Do you charge a upfront diagnostic or estimating fee that rolls into the project if they sign?
• What qualifying questions do you ask to weed out the ARV chasers from the serious buyers?

I’d love to hear how other contractors handle this without burning bridges with potentially good clients. Thanks!