How to InPaint correctly?
Here are 2 guides that helped me understand how to work with inpainting:
My best guess - you using Inpaint Area mode "Only masked" as suggested in many guides. Well they are wrong, and this mode useless in 90% of cases. Most of the time you will work with Inpaint Area mode "Whole picture" because in this mode inpainting replaces things in coherency with rest of the picture.
Example. Removing extra limbs and filling with background (same goes to text removal):
Mask mode: inpaint masked
Masked content: fill
Inpaint area: whole picture
Denoising strength: 0.6-1
Add to negative: extra leg, or whatever you want to be removed. (For text add to negative: text, watermark, signature).
Thus undesirables will be removed and replaced with background that will be coherent with rest of the picture. Note: often after removal you can see crappy details like blur or bad lines, those can be easily fixed in img2img with low denoising (around 0.4) or with additional round of inpainting.
Tip from my personal expirience: watch for shadows. If you've struggling with removal (changing) of something - check if this object have individual shadow in the picture. If so - inpaint object with his shadow, because SD wont allow you to make any considerable change you wanted while shadow of the object present in the picture.