A general rule of thumb that has worked for me....ifnit is heirloom variety at store you can harvest seeds from the veggie ot tomato.
The non heirloom ones are a waste of time....some types of veggies will be ok but mostly you get nothing or you get some mutant that is useless.
However I am not an expert.
Thanks was just wondering. I do have a six foot tall bush kinda thing from a grapefruit seed I planted a long time ago.