Product: Other financial service

I received emails and text messages about purchasing XXXX XXXX products for a customer that supposedly found me in a XXXX XXXX Catalog. My business is online and XXXX XXXX does have catalogs where they mention employees. It seemed believable. We discussed the product she wanted for a {$200.00}, and I never had the opportunity to explain the total with tax before the check had arrived by mail to my address, the address I gave her, from her Employer, an XXXX in Texas. The check amount was for {$1600.00}, and seemed believable for a 2 week pay period in an XXXX. 

When I saw the check amount, I told her I only accept exact amounts which I would be happy to calculate out for her in the future. She blamed her boss for misunderstanding her and delivering her whole paycheck to me. I said when the check cleared at my bank I would make the purchase and give the rest of the money back to her through an online transfer to the account info. she gave me. {$300.00} of the funds were made available to me from my account within the first hour so I made the XXXX XXXX purchase for her though my online store with XXXX XXXX after registering her as a customer and said I would need the account info. to electronically transfer the remaining money back tomorrow when the rest of the funds became available. 

After the customer asked me to send the rest of her money to her family for medical bills and I refused to send cash in the mail, stating it was unsafe and that she was asking me to step outside my boundaries as a XXXX XXXX Consultant in which my responsibility was to place XXXX XXXX orders and ensure that they were delivered to her, not run errands or do favors for others, she gave me an account number. I transferred the money to the account number she gave me. The check bounced after she received her product and after her remaining funds had transferred to another account electronically online, creating a negative balance in my account which the bank now holds me responsible to pay off. 

I am in disagreement with being held responsible to pay this balance off because I do not think the bank should allow funds that are not yet checked to be sufficient through their routing numbers to enter into my account to be used. When the money was made available to me, I thought that meant the money had cleared or had been checked to be sufficient and secure to use and spend. 

While this situation was occurring, another women contacted me about XXXX XXXX and also sent a check for an amount way too high, {$2200.00} to be exact, which the bank put on hold for nearly 2 weeks to double check for fraud. These funds never cleared and I never spent any of the money. 

Why did the bank clear one check and not the other? If I can not rely on the bank to scan the checks before allowing funds to enter into my account, then I want to know how I am to know, running an online business that just started, how I am to know whether or not a check is fraudulent? Obviously this situation only needs to occur once for a person to learn their lesson and change their check policy, but without prior exposure, experience, awareness, or knowledge of all possible scams out there, how am I to know a check coming from an XXXX is fraudulent if my bank is allowing the funds into my account? On top of that, Bank of America should not have allowed overdraft fees of {$100.00} to accumulate on my account due to the fraudulent check. Again, I do not think I should be held responsible to now pay my negative account balance.