Yes those leaves will die off,that is normal.Every Squash I have ever grown has done that.

It is a fungus stem rot commonly caused by one of 3 or 4 various soil-borne fungi. Probably pythium in this case but no way to know for sure without culturing it. See article linked below. The original problem/cause was using soil/dirt/sand in the container rather than a soil-less mix. That is never recommended as it is not sterile, already infected, and creates the perfect conditions for the fungi to multiply and infect the plant. It is then further compounded by way over-watering poorly draining soil. The roots become infected and it progresses up the stem to slightly above the soil line and into the circulatory system of the entire plant. Saving the plant is very unlikely once the symptoms develop to this degree. Sorry. Dave http://plantdiseasehandbook.tamu.edu/problems-treatments/problems-affecting-multiple-crops/stem-and-root-rot/

I so get the panic part 😂😂 I've acted in panic a couple of times too, but almost every time i made things worse. I'm not sure what the "wet" is on the edges, since I have never seen it on my peperomia before, but i do know that peps like to dry out (to a certain extend ofc) and are very hardy! I've had peps overcome colddamage, underwatering, heightaccidents.. it's overwatering that kills m fast in my experience. Watering it, repotting it and then watering again is possibly a bit much.. give it time, peps bounce back easely!

if i got a plant yesterday.. i would water it properly.. and ignore it for a couple weeks and let it settle into its new home ... i would try not to love it to death ... if you are truly unhappy with it.. return it ... yes.. it appears to have some shipping damage.. from grower.. to seller.. to your house.. nothing to do about that .. as long as damaged leaves are green.. then can convert light to energy ... no need to cut them off.. until they go all brown .. nor would i give it a severe hair cut the day after i got it.. just have patience.. and see what happens ... right now its stressed.. not hungry.. no need for fert ... i would also assume.. that a good grower will have treated the plant for myriad of issues.. prior to sale to seller ... perhaps you are seeing old damage ... but unless you see some actual bug or problem do not treat it for anything. ... those few scars as you call them wouldnt bother me.. unless i noted them increasing .. in other words.. i suspected an on-going problem.. and not just a suggestion of a prior problem ... just water it properly for a month .. and 99% of the time.. the plant will be fine ... again.. if you just cant deal with it. take it back and talk to your seller .. perhaps look at similar stock.. and see if yours is the only one with problems... i probably wouldnt waste the gas ... especially if the gas would cost more than the plant did ... ken