My profile now showing -2 and I did not do any exchange. Why some people do this type of things? What do they get from it?
Your profile is not showing a -2, it's not showing any score.
Negative trust is tricky, some people use it as a weapon when they get upset. Did you do something to upset The Pharmacist? If so, maybe you could talk to him and try to smooth things out.
People that give negative trust get nothing out of it.