DO NOT deal with this guy, he takes tenants money and keeps it

I was contacted by Greg to list my cottage, he has never been to the property and i had to deal with tenants he sent, he has been unprofessional in dealing with tenants. I declined a tenant and the same tenant has been coming to my home and threatening me because he says he has paid Greg a deposit and Greg will not pay him back. After declining the tenant Greg informed me that he has someone else that are currently signing a lease, but Greg asked me if the Tenant i declined can come and view again the next day to show his partner, i was confused and told him no. Now i am sitting with a problem and the tenant i declined is very upset and has no way of tracing Greg. DO NOT DEAL with him and do not pay him any money as you will not get it back, not even sure if he will place you.