writing - Job Titles Capitalization

The rules for the capitalization of job titles are not very clear.
After I've read some internet articles (for instance, this Capitalization of job title question) I compiled some rules:

a) It goes before the name of a person:

Professor Adams or Director Joe Brown.

b) It goes immediately after the name of the person:

John Williams, Chairman, will attend the meeting.

Note: if it has "the", we do not capitalize:
Mrs Smith, the chairwoman of the company x, is retiring.

c) In signatures lines at the end of a letter or email:

Sincerely,
Sarah Stevens, President

But then, while browsing a well-known job search website I saw ALL the job titles capitalized in the jobs descriptions:

We are seeking to recruit an exceptional individual as Office Manager for the Registry team.

We are seeking to appoint a number of Teaching Assistants to support pupils' learning and to raise attainment.

and in a common English grammar book I see:

What do you do?
I am a receptionist.

Can somebody explain me the right to way to capitalize a job title?