Risks are always present in trades. Even with established traders, there's are still risks that neither party can control, such as lost packages in the mailing process. You can counter this with purchasing adequate shipping insurance and tracking if possible.
Best to trade with established people to mitigate any shadiness.
Though in the event of trading with people with little to none feedback/reputation, then it's a good idea to have them ship the item first. After receipt of their item, then you'll ship your item. However if you're the one who is new, without any feedback/reputation, then you may have to send your item first. If one disagrees with this trading scenario, then it is not worth the risk. DONT DO IT.
Otherwise if both parties are trusting each other, cross shipping on both ends at the same time is okay.