I sell 4* champs.
I know this will be blasphemy to some of you. But selling 4* champs if they aren't duped isn't the end of the world. I honestly believe its a decent idea, But only if you take them to r3 first and you can afford to waste the other resources that it cost to rank them.
You net more 5* shards by selling champs at r3 than you would by pulling the same champ 6 times.
There are several champs out there that I take to r3 for level up events and immediately sell for the shards. Mags mn, she-hulk, SG, OML, Joe Fix it, Ms M (KK) and the list goes on.
The name of the game now is to maximize 5* shards. And this is how I do it.
Example
She hulk r3 sold for 425 shards x 6 = 2550 5* shards
She hulk pulled and duped 6 times= 275 x 5 =1375 5* shards
then at max sig you (potentially not guaranteed) would get 275 more shards per pull with the max sig crystal = 550 shards
So you would have to pull She hulk 8 times to equal the same amount of shards and selling her 6 times.
If you sold her 8 times you would still be at 3400 shards, so you still would be ahead a thousand shards.
Basically selling 4*champs are only worth it if they are at r3.
I however don't think selling them at r4 is worth it with the current shortage of t4b and t1a.
I am now bracing for the sure to ensue roasting.