Remain standing until told where to sit. Personal relationships are crucial to conducting business. Relationships are based on respect and trust. It takes time to develop a comfortable working relationship and patience may be a necessary cross cultural attribute. The first meeting often takes place over lunch or drinks so your Thai colleagues can get to know you. Business is not discussed on this occasion. Thais are non-confrontational. It is rare for them to overtly disagree. Hence, bear in mind that "yes" may not mean agreement in the way most westerners understand the term. It may mean, "I am saying this so you will stop talking about the subject".