The real thing to worry about isn't asking - it's *how* you ask. A lot of people frame it like they're doing the company a favor by negotiating, which puts them in a weaker position. You're not being greedy or demanding; you're having a professional conversation about your market value. The company already decided you're worth hiring, so they've already factored in some flexibility.
I know someone who got an offer they thought was decent but didn't match their experience level. They asked if there was room to adjust it, kept it friendly and brief, and the company came up about 8% without any pushback. They almost didn't say anything because they were nervous about seeming ungrateful. On the flip side, I've seen people accept lower offers and spend the whole first year feeling resentful about it - that tends to show up in your work quality and how you feel about the job.
The key is doing it right after they make the offer but before you formally accept. A simple "I'm excited about this role. Based on my background and what similar positions pay in this area, I was hoping for [number or range]. Is there flexibility there?" works. If they say no, you're still hired and can take a breath and decide if the offer's still good to you. But most places will negotiate a bit if you ask professionally.