Unlike jarred or canned salsa, restaurant salsa is essentially small-batch, freshly made salsa. These establishments have access to high-quality ingredients and equipment to streamline the salsa-making process and ensure a consistent product. Restaurants have ingredients delivered fresh daily from highly specific purveyors, giving them access to the freshest and best quality of even the most obscure ingredients.
Recipe developers for restaurants have plenty of time to experiment with salsa recipes, testing them and perfecting them before they even reach the menu. Salsa recipes have specific spice and ingredient proportions executed in an almost formulaic manner.
Furthermore, many Mexican restaurants are either owned by Mexican families or run by Mexican chefs who rely on both generational and cultural knowledge to create the most authentic salsas.
Making the salsa from the ingredients the same day you buy them will further ensure restaurant-quality freshness. The same goes for spices and seasonings. Buying whole spices and fresh herbs will result in more vibrant flavors.
Of course, making the salsa to order and eating it fresh out of the blender with hot chips is as close as you'll get to the true restaurant experience. In some cases, letting the salsa sit overnight in the fridge gives it time to develop more complex flavors.