I was thinking that a interesting way to stop this would be to have all trades deals finish before the cash could be spent on anything else.
sample ... 3m/50t deal seller accepts then must buy tech or use stock to fill order. Can't do anything else until this is done. Buyer will get order filled message, the filled order will ship automatically in 10 days. Seller will be able to use this tech for the good of his empire, but it will not count against him so he can buy from zero for his other trades... Seller will also know how much he has left to spend as the new balance will be added to his cash.