You buy 40,000 coins for 10 dollars. The next game you play is set at 10,000 coins and even though you try to live they charge you 10,00 coins for a game you did not play. Most game are for 100 coins but when you buy 40,000 coins they go into a scam mode and try to cheat you.
As far as I am concerned the people who run Rummikub online on the pc are a bunch of thieves who are here to steal your money. I rate them as 0.