"He should sell computers, he is good at it."

Translation: Powinien sprzedawać komputery, jest w tym dobry.

[Nhcuongplus]

Too many errors like that: I wrote "On powinien sprzedawać komputery, on jest dobry w tym." - And wrong :(. Please add a variant.

[Jellei]

That really doesn't sound natural. First of all, the repetition of "on" is maybe not incorrect but at least not natural, and the word order in the second clause - I don't think a native would say that.

[deactivated user]

Is "w tym jest dobry" a possibility, or is it only "jest w tym dobry"?

[Walkinthedog]

Why is there no on for he? I always hear it used as a kid and it messes my mid\nd up now.

[Jellei]

"powinien" already means that the subject is masculine (3rd person singular masculine), "on" can be used but it's absolutely not needed.