Occasional trades of guns for services rendered: Good, fine, and legal as can be.
Regular trades of guns for services rendered: Bad, and most likely illegal.
Report the values on your taxes if required by your business type, and only accept gun trades from people you know well and have a good business relationship with.
As long as you're only doing this once every few months, you have nothing to worry about.
And don't sell the guns. Only accept guns you want for your personal collection, don't take a gun you don't want and will have to turn around and sell.
"To preserve liberty, it is essential that the whole body of the people always possess arms, and be taught alike, especially when young, how to use them." -Richard Henry Lee, Virginia delegate to the Continental Congress, initiator of the Declaration of Independence, and member of the first Senate, which passed the Bill of Rights.