To all the experienced consultants:How do you spot time-wasters early on? You know the sort - they make you jump through 100 different hoops on the off-chance that you might get a bit of work out of them, and then you find out that they're also speaking to 10 other companies and the contract finally goes to the one he used to work for (for instance)?These people seem to have a knack of presenting themselves as credible/legitimate, then almost always deliver some devastating and almost impossible to predict blow when you least expect it.I'm not talking about the sort where you know you're in a competitive situation and handle it accordingly. Instead, I mean the sort where you know its's competitive, but then in hindsight realise they had already made up their mind before they even started talking to you.Any tips/ideas?

Learn to sell.

Qualify your opportunities. In the situation that you've mentioned, if you know they've got an extremely good relationship with their existing supplier, chances are they're using you to push their prices down. You would if you're the client. If it's not worth investing your time and effort in, pull out. Invest your time in other leads that have a higher chance of converting into sales.