Recruitment isn't easy. How can you predict how good someone will be until they've been doing it a while? But there are some tried and tested ways to weed out wrong folks early.
1 Ask the receptionist.
If the candidate doesn't leave a good impression with your receptionist, don't hire them. If they aren't able to make a good impression when they're really trying, they'll be hopeless when they relax.
2 Just don't use the words should, would, and could.
All they teach you is how good the candidate is at answering hypothetical questions.
Instead, get stories about how they've reacted under specific circumstances in their past. Ask "Tell me about something in your career you're proud of." Then drill down, look for STARs:
Now ask "Tell me about something in your career when things went horribly wrong." Then drill down again, look for STARs, but in this instance you'll find out how they reacted to stress, turned things from negative to positive.
3 Do they talk with interest and authority about your industry and market sector?
The folks you really don't want are those for whom this will be just another job. Good people are interested in the trends in the sector, how your market works, the products in it. With the really good ones, you're just privileged to pay their wages while their career passes through your company.
4 Ask yourself: Would I like to spend an hour in the pub with this person?
If not, then will your existing staff, prospects and customers like them? Probably not - so are they a good bet as an employee?
Good interviewing doesn't mean you spot the great ones easier, but it does mean you can weed out the wrong ones with much greater certainty.