This supermarket is our fave Mexican market and carniceria in Seattle we have been coming here for…read morethe last two years consistently, we're here every few months to stock up on key ingredients we can't easily find in the city: Papaya, Nopales, Knorr Chicken Flavor Granulated Bouillon (Consommé--it's pricier at Safeway/QFC, etc..), religious candles, dried Chile de Arbol and Guajillo, Maria's cookies/crackers, Tomatillos, Tapatío, Yucateco, Valentina, Chamoy, and Abuelitas hot chocolate tablets. Also, other things, but those are the staples. [they have yummy pan dulce, cakes and desserts, and all the chips you can dream of, some imported from MX Direct]
The location could be better, but they have a private lot, and we haven't had any issues in the two-plus years of coming here.
Most items are reasonably priced, and the folks here are helpful and welcoming. There could be seedy characters around, but most mind their business.
We tried a few other markets closer to our neighborhood, but their selections weren't as good as Castillos. Castillos has most things you can dream of and their carniceria is also bomb, we've tried most meats here, they're pretty high quality. The only con here is the price of the meats, but it's understandable that since they're a small market, they're less competitively priced than the larger grocers. Also, I don't want to hurt their reputation by getting into the details; all I will mention is to be very careful with the Chorizo. Make sure you chew it thoroughly and inspect it carefully while cooking.