Adam Clarke on Deuteronomy 26:14

I have not - given aught thereof for the dead - That is, I have not consecrated any of it to an idol which was generally a dead man whom superstition and ignorance had deified. From 1Cor 10:27, 1Cor 10:28, we learn that it was customary to offer that flesh to idols which was afterwards sold publicly in the shambles; probably the blood was poured out before the idol in imitation of the sacrifices offered to the true God. Perhaps the text here alludes to a similar custom.