You're right that tactics may be dubious, and this is a big concern of mine. We actually had a client at the place I worked (before freelancing), come in and ask if anyone was knowledgeable in black hat techniques. We all worked to educate him as to why it was a bad idea but he pressed forward.

It only took about two days before Google banned him. A few hours at the top of the search engines, and it was all gone.