Contact which is both Organisation & Individual
I would rather think like this:

Something he/she is --> contact type

Something he/she does --> group

If he is a person, then the contact type should be Individual. Maybe he works with or owns an Organization, then create a relationship.

To be a lecturer or an advertiser can change ( if he change job), but he will always be an Individual.

So to me it gives more sense to create two groups called Lecturer and Advertiser, and put this contact and the others in the corresponding groups.