Tried doing a search, but couldn't find an answer.

I want to know what is the most effective way, other then paying GP, to go ahead and get rid of unwanted planets?

not sure there is a way though.

you can take off all defense, and hope an idiot scans and takes them

sometimes if ur willing to waste an artifact or two ppl may take them, i got rid of a small Minig avrg artifact by dropping 2 Barrier Nexus on it. no other def

Dropping a polychron vault usually entices people also.

Also, if you're Mylarai/Kronyn you can uplift them just enough to be worthwhile for someone to take. I wouldn't waste Talth though.