Many people will try to take advantage of you, from customers to suppliers to employees to business partners. You can swear never to be victimized again, and institute tougher practices to prevent loss, but most of these will alienate the good customers and partners. This hurts business more than the direct damage from bad actors.
Yelp is full of unflattering descriptions of small business owners who treat customers with distrust or arrogance. You often read of restaurants that quickly make diners feel unwelcome, or bike shops whose mechanics and clerks make paying customers feel stupid. I try to avoid such businesses, although I can't stop buying bagels from the grumpy deli owner in my neighborhood.
Only through optimism and the related acts of forgiveness (and perhaps forgetfulness) can a small business owner maintain the positive outlook that attracts customers, employees, and business partners.