We check product before sending and pack it carefully. We understand, that sending it back in case of defect does not make sense, as shipping cost may be the same as product's price.
Sometimes package is opened at customs and small parts (like bolt and nuts) can be lost. Sometimes package can be damaged. We are not responsible for that but we try to solve problem ourselves.
If something is wrong with the order - we solve the problem: resend product, return money, send additional parts.