Charity Navigator rates them four stars. According to their latest IRS filings, they spent over 90% of revenues on program expenses. That's a very high percentage. They're not listed on Charity Watch, though - which isn't necessarily a bad sign, but if they were, it would mean that they'd been through the American Institute of Philanthropy's more extensive review process.

Honestly? I'd never heard of the "Better Business Bureau's Wise Giving Alliance," and they don't have a current report on Locks of Love. Note that the Wikipedia article has no citations for the Better Business Bureau report. As an overall organization, I don't consider BBB to be much more trustworthy than Wikipedia. The Wikipedia article also acknowledges that "Hair that is less than ten inches or grey is separated from the donations and sold to offset manufacturing costs." If most of their donations come in-kind as hair, obviously they need cash to meet their operating expenses, and selling some of the donated hair would be a way to get that cash.

If you have a financial advisor, they should have access to the detailed reports from GuideStar and AIP. I personally don't know anything about Locks of Love, and it's always good to be skeptical when considering a donation, but these are the resources I normally use to check out a charity.