I asked one how it was done - there was an interesting array of phrases including 'cloaking' and 'link farm'. Now that could involve a penalisation or drop from Google. Most of them do not know what they are doing...
When I searched manually for the keywords they had used and on the engines they had stated, they were listed and quite high up.
Maybe they were hoping the email wouldn't go directly to the person who did the optimisation ;)
They do it through doorway pages. So I asked: "Doorways, don't they get you banned from Google?" - "No. We wouldn't do anything to risk our clients" - "www.google.com/contact/spamreport.html" - "Oh, I'll ring you back"
He rang me back. "It means cloaked pages. Google do not allow cloaked pages where <explanation of cloaked pages>..."
It shows that they do not even know the difference between a doorway page and a cloaked page. Even the Google spamreport page has them listed separately.
Remember the important information when these people ring: www.google.com/contact/spamreport.html :)
P.S. Notice the promises they give, they will get you into the top ten within ?? weeks or your money back - guaranteed. They don't say how long you will be kept in the top ten. I'm sure you can all do better by studying webmasterworld for a few hours and save yourself £749.00+VAT and target more than ten keywords.