Complaints - they happen to every business, you cannot get away from them.
There is a saying in a movie [I don't remember which one], that you might be selling the most delicious, sweet and plump peaches in the world, yet there will always be someone who doesn’t like peaches…
It’s just part of the process. Embrace the complaints.
But - do not ignore them
The complaints won’t kill your business, bad feedback won’t take your company down, but ignoring the feedback certainly will.
Don’t negate the complaints or give excuses. There’s no point. If a customer complains about a slow delivery or items arriving damaged, this is your opportunity to seek a better shipping operator. If you heard that the socks you are sending have stitches coming out, it’s your chance to ditch the supplier of faulty products and find a better quality one. You move ahead in the business thanks to the complaints! Embrace them, love them, but never ever ignore them…