In Dungeon World, "coin" is the base currency with everything else listed in terms of it. 100 coins have 1 weight. Many items are worth more than 100 coins, making the carrying of coins very heavy if you wish to buy something nice or sell something nice; you cannot use coins as you cannot carry enough for large transactions.
I've had to introduce a concept of gem-trading with exchange fees (gems cost no weight per the rules.) But then that is a little onerous to track the value of individual gems and exchange fees on coins <-> gems isn't really a fun principle of a game. I'm very close to just removing the weight cost of coins, but am very hesitant to alter a rule of the game as written.
What is a more rule-abiding pattern for respecting the coin weight while also allowing serious purchases/sales that is fun?