Just to add another $0.02, the liquid you were offered is more likely GBL, which metabolises instantly to GHB in the body. Doesn't matter though, cos what Biscuit said was true - you can't trust dosage when sold in liquid form. I personally love the stuff - I'm definitely from the "better than ecstasy" school of thought, but I take it in controlled powder form that I dissolve myself - I would NEVER buy it in liquid off the street. If taken with care and knowledge it is perfectly safe, but the only person you can trust to do this is yourself.
Oh, and GHB is the same as GBH, but I don't know anyone who calls it GBH or Grievous Bodily Harm outside the scaremongering media. Please don't aid with this inaccurate, ignorant propaganda - if you hear someone calling it GBH please correct them. GHB = Gamma Hydroxy Butyrate.
Cheers
Cat