People will give you all kinds of advice about what to charge. The reality is, you charge whatever the market can bear. There is no fixed number that is "right".
If you have customers that you can reliably depend on for work and actually pay their bill, you can often afford to drop your rates some. If you are grubbing for it a few hours at a time, you really need to charge more.
I guarantee you that if you are charging someone $67 an hour and getting ten hours of work a year out of them 2 or 3 hours at a time, you are losing money on that customer.
you might actually make good money if that same customer is paying you $60 an hour for 2 men 40 hours a week for a year.
the numbers are pretty straightforward. most tradesman cost their employers about 40% of their base pay for fringe benefits and government inspired expenses. on top of that, tradesman only work about 42 weeks a year, but get paid for 52 (vacations, holidays, sick time, training, etc.). So if you pay someone $25/hour, your actual cost per hour is about $35 an hour and after dealing with the almost 25% non-chargable time, you are closer to $45.
You might think a long term gig where you are charging $60 an hour and getting $45 for a couple guys is a heck of a sweet deal. However, by the time you pay a salesman, estimator, supervisor, and trainer (even if those people are all you), that $15 can easily evaporate.