There is no guarantee that all your seeds will grow into plants, but most seed banks do have a good accuracy rate - meaning at least 80% of your seeds do end up growing into fully grown plants. This is a risk that you have to take. You might end up with all of them growing up well or none of them, but you are more likely at the safer side of things than the having the latter happen to you. Nonetheless, there’s never any guarantee. Most good seed banks refund you or send you new seeds in case such a thing happens.