The less crass answer: In almost every company, you’re being hired on a salary band, so unless you’re at the top of that band in the initial offer there is room to go up, so you can typically push a bit higher. The trick is to make a request that’s higher than what they initially offer but not so high that they outright reject it without additional conversation, and if they are play hardball, and don’t budge on anything, you just reject their offer. It does mean you have to be comfortable rejecting an otherwise decent or good offer, but presumably most companies are willing to negotiate with a good candidate so this shouldn’t be a problem in practice if the negotiation is done in a considered way.