Costumes vs. Customs
As any fashion buff will stylishly tell you, the word costumes refers to a type of dress specific to an occasion, season, nation, region, or historical period.
The word customs refers to the usual ways of acting in a given circumstance, like a holiday.
Costumes refer to clothing items. Similarly, costumers are people who outfit other people in costumes, like on a movie set. Customers are people who buy things, like at your job at the commemorative spoon store.
If you switch any of these up, the results can be hilarious. But since that's probably not what you're going for in your writing, it's a good idea to keep costumes and customs on your spelling radar.
Before you travel to a foreign country, it's a good idea to brush up on the local customs.
That's some solid advice. While a thumbs up gesture means "good job" in the United States, in Singapore it's the equivalent of sticking your tongue out at somebody, or worse. If you knew that customs is the right word for this sentence because it's referring to acceptable local behaviors, then thumbs up to you (the American kind).
Every year, Reggie wears the same Halloween costume. He's always a "cereal killer."
We can appreciate a good pun as much as the next person, but it might be time for Reggie to switch things up. In this example, costume is the right word because it refers to a special type of dress reserved for Halloween.
Anne works at a fabric store in Santa Monica, and she says some of her best customers are Hollywood costumers.
In this double feature of an example, we have customers, which refers to the people that buy fabric from Anne, and then we have Hollywood costumers, who are people who make imaginative outfits for the big screen.