I wouldn't "give up" like some people here are suggesting. Try everything you can to get out of taking the hair test. Tell them you have nothing to hide but you don't believe that hair tests aren't accurate enough. Tell them you will happily give a sample of your blood (approx. same detection time as urine) to be tested. If they refuse to allow you to take any other type of test, try and stall as long as possible. If you can't get out of it, I wouldn't turn down the job just because I'm afraid I might fail a drug test. If you're honest about taking 3-4 hits and that's within 2 years (last time about 40 days ago), you should be good. Drug tests have cut-off levels for passing and failing. You can still have THC in your system and pass. Ask them (if you don't want to look too suspicious, ask who they are going to send you to and talk to someone that works at the lab) what the cut-off levels are. I don't know if you can even test the exact amounts of different drugs through a hair test, if they can't give you exact numbers, refuse it all you want and offer the other 2 tests, tell them you only trust a test that gives you the EXACT results because you're afraid of false positives. I have no idea if those shampoos work but hell it couldn't hurt to try.

Edit: Fixed a spelling error