Quick answer
One man's work is a trick; the other's is planting. The difference is whether the result is real when it arrives.
Read both lines
The contrast is between fake work and farming. "Deceptive work" describes earnings that look like earnings and are not, gains built on a misrepresentation that will eventually be discovered. Against that the verse sets sowing, which is slow, unglamorous, and honest, and calls its return sure. That word is the point of the verse: not large, not fast, but reliable. The book keeps recommending the slower thing on exactly this ground, and the agricultural image will return in the next verse and again at verse 30.
Related: Proverbs 11:30 · Proverbs 13:11 · Galatians 6:7–8
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.