Are these professionals you're hiring or college noobs? If it's the latter, you need to cut them some slack.
I have to agree here. There is a big difference between hiring a guy who has allegedly been in the real world for 20 years vs. a new college grad. If you're hiring college kids, the important thing to look for IMO is work ethic. Look at their work history. Talk to their former employers. You can teach a kid what they need to do to do their job, but you can't teach them a good work ethic.
Now, with that being said, I've interviewed a ton of "experienced" candidates for positions in my day. Some of them were just frightening. One lady was so bad that they STILL refer to her BY NAME at my last company, and we interviewed her probably 5 or 6 years ago! We were interviewing for a help desk position, IIRC. For all IT positions (programmer, systems engineer, help desk, etc), we gave the candidate an assessment test along with an interview with technical questions or scenario-based questions.
This girl was incredibly bad. She was a referral from an employee, so we had to interview her, but her resume didn't look bad so we thought "what the hell." She couldn't answer any of our questions. One question I asked was "Let's say Jane Doe from accounting calls and says she can't print to the network printer. What would you do to troubleshoot?" Her answer? "I'd call the network admin." WTF? We poked and prodded and tried to get her to provide detail on what she would do, but even if she did manage to give us something she'd try, step 2 was always "Call the network admin." She answered that for several questions. We also asked her what her career goals were. She said: "I am working on an A+ certification." We said "Good, do you have any plans to look into Microsoft certifications?" She looked at us like we were speaking a foreign language and said "No." No qualifiers, no explanations, just "No."
Because of her, we instituted mandatory phone screens for ALL candidates before bringing them in for interviews.