The Thai lottery is a rip-off. Pure and simple. Even if you manage to hit the jackpot you only win 4 million baht. A ticket costs 2 quid!
The underground lottery is slightly better. The odds for choosing the two numbers is 59-1 instead of 99-1 (true odds).
Best way is to buy one ticket maximum, just for the fun. Anyone who buys lots is throwing money into the fire.
As far as I know (don't quote me), the Lottery pays back 60% in prizemoney, not a very good return. I think it is in very small print on the back of the ticket.
So if you buy a "double ticket" at 80 Baht, 48 Baht is returned to the players and 32 Baht is retained for overhead and profit.
Problem now is that in many places the ticket sellers want to charge 100Bt, an extra 25% of the ticket price. So if you pay this price, still 48 Baht is returned as prizemoney, so only 48%.
The government was looking to incorporate a ticket vending service via the banks' atms. Don't know what happened about that. If that happened, I wonder if the price would be the proper 80 Baht?