Hi, this is planet Earth you have landed on.
We have websites that sell cheap things, such as: Amazon / Ebay / AliExpress.
They sell cheap things that can have counterfeit components, low quality, not certified things, stupidly exaggerated accuracy numbers, and so on. Sometimes a factory rejects a batch, and those might show up on those websites.
Some sellers tell anything to sell something.
There are companies that started cheap but aim for better quality, such as Elecrow. Those products cost more.
There are also good companies that give good information and won't let you down, such as: Adafruit, Sparkfun, Pololu.
Manufacturer's page of the muRata SCA3300 : https://www.murata.com/en-global/products/sensor/accel/overview/lineup/sca3300.
Manufacturer's page of the TDK / Invensens MPU-9250 : https://invensense.tdk.com/products/motion-tracking/9-axis/mpu-9250/
They are in the range of 3% or 1 degree accuracy. That is the range for MEMS sensors.
When they are calibrated and a processor is added, then it can be better. If a well known brand that you trust gives certain numbers, than you can trust it. However, everyone can made ridiculous claims on those websites.