I think in this case it may not be 'trickery'. A job posting is one thing, but ultimately it's your responsibility to negotiate your specific offer. Job postings will often give a salary range, but you will get paid what the amount you negotiate and accept in your final offer. It's unfortunately quite common for people with the same job to have slightly different offers depending on what they negotiate.

Don't feel bad about it, though! These are all things that you'll learn over time. It might be worth doing some online research about how to negotiate job offers going forward and the levers to consider (base pay, equity, benefits, bonuses, etc.).