Thailand's high season for tourism has just begun, but the signs for many in the industry are worrying.  Experts are blaming higher fuel costs, global economic problems and political unrest in Bangkok.  In September, arrivals at Bangkok's main airport were down 21 percent, and industry experts say numbers are expected to remain low as the global credit crunch prompts consumers worried about their jobs and mortgages to stay at home.  Meanwhile, the Tourism Authority of Thailand is trying to entice tourists from Southeast Asian markets like Singapore and Malaysia, which have so far managed to avoid any serious impact from the global financial woes.