How do you hire a good WHITE HAT SEO company from BHW?

I haven't bee in the market to purchase SEO in years. At this point I need to buy whitehat SEO because I cannot afford to lose my business to blackhat techniques. How can I be careful when buying SEO that the company I am hiring is using quality links? I have purchased SEO in the past as a reseller for a company that showed really good results. They were blackhat and eventually I lost rankings for clients and some were removed from Google. I don't want this to happen to me.

How do I know…

How do you hire a good WHITE HAT SEO company from BHW?