Deceptive SEOs usually display the following characteristics:
1. Send unsolicited emails. Reminding you about your poor ranking in search engines and how it can be improved by them.
2. Are owners of shadow domains. A shadow domain is a site that simply tries to funnel users to your site by using redirects which are deceptive in nature. If your relationship with the SEO sours or terminates, then the SEO may take his revenge by pointing the shadow domain to your competitor's site. All your traffic, for which you have paid the SEO, shall now be directed to your competitor. Dishonest SEOs may also take money from your competitor's for this.
3. Create doorway pages. Doorway pages are pages with a lot of keywords. Getting more keywords in a page does not promote search engine rankings. The deceptive SEO will try to sell you that a wide range of keywords can help more search queries. But it is logically wrong. As individual pages can never display a wide range of topics. Why they sell this to you is because, they create hidden links pointing to their other clients, within the keywords. It may be possible that these hidden links point to sites with illegal or unsavory content.
4. Sell keywords in the address bar. Many SEOs try to sell you software by which you can type keywords directly in the browser address bar. Not all users have bought such software and their self-reported buying number should be taken with skepticism.
5. Consider actual results and ads on the same level. The search results page shows actual result and ads. If you pay for an ad, then you may see your ad being displayed in the top level search pages. However, that is an ad and not your actual listing. Moreover, there is no guarantee that your ad shall come again in the top level pages. What matters is your actual listing in the top pages and not your ads in the top pages.
6. Gives a guaranteed ranking provided long keyword phrases are used. This is false. Nobody can guarantee a ranking in any of the search engines.
7. Has false WHOIS info or has multiple aliases. Such SEOs are the worst amongst the worst.
8. Uses scumware and spyware to get traffic to your site. Your site shall be banned by all search engines.
9. The SEOs own site is poorly listed by the search engines. If the SEO cannot make his own site good enough, how can he make your site good?
10. Does not mention any refund clause in the contract. So if you are cheated, you have no legal option. Be sure to include a refund clause, so that you can legally claim a refund.