Well, how can these companies calculate my IP address? Is it possible to advertise one company from several accounts. How does this affect the company? and one more question. can I buy or sell an account officially? by forum rules
*sigh*..
They usually look at your post history and the adresses you used, to see if there's any correlation between them. It is actually fairly easily to distinguish how someone types aswell, although i don't think this technique is often used.
Is it possible to advertise one company from several accounts
Depends on the campaign, but usually not. If they find out you will probably be banned from said campaign. ( and tagged for abuse)
How does this affect the company?
Gives them a bad reputation and generally a lower level of post quality from their members.
can I buy or sell an account officially? by forum rules
Yes, you can, but it is highly frowned upon, and will usually earn you a nice red trust from DT2 + DT1.