Who sells THETA?

Could you please provide a brief explanation in English about who sells THETA? I'm particularly interested in understanding the various entities or platforms involved in the sale of this cryptocurrency. Could you also elaborate on any specific conditions or requirements that might be associated with purchasing THETA? Additionally, I'm curious to know if there are any specific markets or exchanges where THETA is commonly traded, and if so, what are their reliability and reputation? Thank you for your assistance in clarifying these points.