I don't understand this. Why not trying the "shady battery" for cheap before buying a whole new phone? Even if you somehow don't trust their batteries, I see s10e batteries on ebay for ~10€. Just buy one of those and have them install it?
Every device I've ever wanted to keep after its battery started degrading (mostly laptops, but has happened with a phone too) I've either ordered one from ebay and replaced myself or went to a cheap local shop.
I've had friends take their phones in for a battery replacement, and let's say the results were not better than before they took their phones in.
As with buying a battery from ebay, it's still not gonna be an OEM battery (or am I wrong?). OEM stuff is more important for phones than for laptops, I have found
Every device I've ever wanted to keep after its battery started degrading (mostly laptops, but has happened with a phone too) I've either ordered one from ebay and replaced myself or went to a cheap local shop.
OE batteries aren't magical.