One tip: The position of the person making the inquiry seems to matter quite a bit.
For example - product manager, sales manager, shipping department --- I've often seen these types of inquiries come from someone newly hired at the company who sits down at the keyboard and starts emailing everyone they can find who may remotely be able to assist.
Inquiries from owners, CFO, CEO, Accountant/CPA tend to be several rungs higher on the ""may actually pay something"" scale.
I schedule a one and done conference call with them after which they're free to decide if they want to pay for a review or continue browsing the web for a freebie.
I've learned not to fall down the rabbit hole of logging to their system and ""taking a look"". I'm also finding a higher percentage appear to largely be looking for free second opinions on whether they should switch VARS or stick it out. Many of these types are on MFG and/or JC and can't believe their VAR isn't a miracle worker who can take a long neglected module like WO/MRP/JC and make it sing.....
Also seeing some end users on double digit numbers of integrations/enhancements bewildered that there's not one person at their VAR Who is an expert at each and every integration they've been sold. Operative word being ""sold"".