Make sure whatever you are trading has equal or fair value so as not to take advantage of anyone else’s misfortune or lack of knowledge regarding a certain item’s worthiness or quality .

This hadith speaks to the importance of understanding and appreciating the value in things we exchange or trade with one another. In this particular case, Sa'd bin Abu Waqqas was asked about buying wheat with barley and he advised against it because wheat is more valuable than barley and so exchanging them would be unfair to whoever is receiving the barley in return for their wheat. Similarly, when someone asked him about buying fresh dates with dried dates he said not to do that either because fresh dates decrease in weight when they become dry which means that whoever receives dried dates will be getting less than what they gave up for them originally if they exchanged fresh dates for them instead. This hadith teaches us that we should always make sure that whatever we are trading or exchanging has equal or fair value so as not to take advantage of anyone else's misfortune or lack of knowledge regarding a certain item's worthiness or quality.