If I had created extra accounts that I rarely used apart from raids and one of them had a Mewtwo, then I would perhaps sell it if the price was $500+.
But I only have one account and I've worked hard with that one for over a year now to reach lvl38. There's no way I'd even think about selling that one for $500.
Even if I get bored and stop playing the game I might not sell it. Add another zero to that amount and maybe I'll consider it, but only if I decide to stop playing.