If they discourage regular software updates—such as for WordPress—they are leaving your site vulnerable to security breaches.
Use of services like "domainsbyproxy" to conceal ownership information can be a warning sign.
Reputable webmasters often have an About Us page with real photos and backgrounds rather than generic stock images.
A trustworthy webmaster should be able to clearly explain their process, including how they handle security patches and software updates.
Google Webmaster Trends Analysts Q&A Interview - Aleyda Solis
They should be easy to contact via discoverable contact details or even a toll-free number, which is rare for scammers. Red Flags to Watch Out For