Rccrystals hold on - are you telling me that when you get an unknown substance, you have nothing to loose? Cause it was free???  What about the most important thing - customer safety? I know what you mean money, but it does not sound that way. And please rethink your sampling approach, if you expect no criticizm, not because quality is good, but given it was a free sample, your way of thinking does not fit here. You should be open for each constructive feedback, as each of such is an opportunity to improve. This is how you build relationship, and customers are your biggest assets. Treat them fairly, be transparent and listen to them. And be humble, as actually you have sth to loose - I bet you know that acquiring a new customer costs 5-25 more than retaining an existing one. What's more interesting, increasing customer retention by just 5% increases profits min 25%. 

Please note that sending samples is your decision and you must accept the risk of potential negative feedback. Instead of ignoring it, you should take as much as you can. Position yourself in a way that this is added value for your business. Small change in a way of thinking, but in fact critical.

This is just my input for the way you are doing business. End the end of the day, you are in charge of defining strategy and execution 😎