If you bought a genuinely inappropriate bike for your terrain or poor fitting, or you realize you bought something way too cheap, that's one thing, but it'd honestly be hard to have an informed opinion about what you'd actually like out of a mountain bike. Particularly on full suspension bikes, some of the characteristics in suspension kinematics or handling that you'll think feel good as a beginner will not be what you want as an intermediate or advanced rider. For geometry, for example, generally speaking faster steering bikes feel good to a lot of beginners because they're more familiar (relating to older MTBs or road bikes) and because they're riding at frankly much lower speeds, and they hold a line uphill more easily and can be easier to carefully pick a line at low speeds descending, but their lack of stability can feel really scary at speed. For suspension kinematics, a lot of beginner riders won't be pushing the bike hard enough to get a feel for how it feels from its midstroke through its end stroke on a mid travel trail bike.