Kozlok

Either your camera or lens is defective or you could be setting something incorrectly. What level of experience do you have with photography? ILC cameras like an XT5 assume the operator is skilled, and the settings allow for a wide variety of choices. If you aren't familiar with settings and modes, it's quite easy to take bad photos with a good camera. You should become familiar with your camera before accepting paid work. For example, one setting is Focus Priority vs Release Priority. When set for release priority, the camera will take a photo as soon as you press the button. If it's set to focus priority, the camera will not function the shutter until focus is confirmed. If you set AF+MF to ON, then you get release priority, even if the camera is set to focus priority. There are many other modes that affect how the autofocus behaves. Continuous vs single vs manual mode, face detection, pet detection, etc. Another problem is if your shutter speed is too slow, the image will appear blurry even if it is focused correctly. If the ISO is too high, the image will be blurry even if everything else is correct. If you choose the wrong aperture, your images can be blurry. For one of your images that is "bad", maybe post it here with EXIF data so we can offer advice? Also, maybe watch this video

I have used disposable lens cleaning wipes to remove this kind of residue before. Get the zeiss brand, they tend to work best. I use a q-tip instead of my finger to push the wipe around because my finger is way too big. Usually have to do it 3 or 4 times. Be gentile and slow. If you get any cotton fuzz from the q-tip in there, use a proper rocket blower to remove that. You can also try something like a lensPen. I have one of those too, but generally prefer the wipe method above. In the future, to remove dust, I prefer to use an unsized nylon brush. You use canned air on the brush, and this charges it electrostatically. Then wipe the brush over the sensor and mostly the dust is gone. You can get the brushes typically on ebay or Amazon. To check for sensor dust, take a photo of a clear sky at f22 or as high as you can go, at ISO125. Then use spot detection in Lightroom. Brush again if dust remains.