Need a detail description about what is the quality issue is

Hello,

You need to adjust the white balance, and I would recommend some cropping. As mentioned, there is too much negative— empty space—around the subject.

You need to have good lighting and exposure.

You can make a lot of corrections in photo editing software.

1. Too much background in proportion to subject. There's too much empty space.

2. White balance is off.  On the RGB scale, true white is 255, 255, 255. Your white is skewed to blue 214, 212, 224.

3. Histogram shows too many highlights and no shadows or midtones. 

Calibrate your display to ensure an accurate representation of your work. 

Too much dead space around the images. While blank space is always a good idea to allow for adding text. While you do leave room to allow the buyer to crop in any direction, doing so yourself with potentially increase chances of the assets being sold. In addition, the background is not white as you've described it here. You should also submit your assets in sRGB color space.

Exposure, lighting and composition issues in each of these.

M, the colors in these two photos is way off, too much magenta and have no contrast. 

There's no need to look at the histogram to see the photos have poor quality. 

Tip:

protect your lens from light contamination and flare. If you're using a lens shade it's not enough. Make black cardboards, black fabric or make a black cylinder and place it around your lens.

Learn to use tools in Lightroom and Photoshop that help you clean white backgrounds...

And demand a lot more from yourself!

I do not think that the background is white. Is your monitor calibrated? Also, the subject is too small. Contrast is also lacking.