Is a Nicoise salad hard to get right?

It's honestly more about the quality of your ingredients than any fancy technique - that's the one thing I've learned from years of trying recipes. Use good canned tuna in oil (not water), proper Niçoise olives if you can find them, and don't skimp on the anchovies in your dressing; they're key even if you don't think you like them. The dressing itself should be pretty simple - just good olive oil, red wine vinegar, dijon mustard, garlic and those anchovies - nothing complicated. I'd bet the delis you're going to are using better quality versions of these basics than what most home cooks grab, so try upgrading there first before you change your method.