Western men are rich
Most Thai girls believe Western men to be rich, and has already been stated, this is often the case in terms of relating the average earnings of a Westerner with the average Thai male. In some cases the woman will agree to the marriage simply for the money, and such marriages are certainly not made in heaven. They often end in tears and the loss of a great deal of cash by the man.
However, you should be able to tell if the girl you have chosen feels the same about you. Thai women fall in love with western men just as they do with young people from their own country, and while the initial attraction might have been your wallet, it might not be why they marry you. You should take the same time to get to know them as you would a girl back home. Many American and European women will fall for a very rich guy - you just have to learn to tell the difference!
Family obligations
Most Westerners fail to understand the family ties of Thai women. For some women, marrying a foreigner is a way out of certain poverty for her and for her family - even if she does love you. This is not a mercenary obligation as many Westerners claim, but is simply an example of the close family relationships that exist between the members of Thai families: if a Thai bride has married a moneyed groom, then the family would expect to be cared for, even if the groom was a Thai. The same would be true if a rich woman married a poor Thai man. You might feel the same if you married a wealthy Thai woman.
The Dowry or Sin Sod
The dowry, or sin sod, is an integral part of Thai culture and how love works in Thailand. It is intended as a gesture of honor to the Thai bride's family for bringing her up well. The dowry also signifies that the groom is able to look after his bride financially. The average dowry you would expect to pay for an educated young woman would from $3,000 - $10,000, though some ask for up to $30,000 and more. More than $10,000 for a university educated Thai bride is excessive. The dowry is today generally no more than a symbolic indication of the wealth of the groom, and returned in full, or sometimes in part, after the wedding