Can you buy a permanent buff with CSC/sP? I never realized how useful this is.

are you talking about the discount on npc shops? if so, yes. you can buy discount cards that give you a permanent buff as long as you have it in your inventory (you can lock it)

they are expensive though, and i think it takes a lot of restocking for them to actually be worth it (i'm not a restocker though so if someone who has more experience with it wants to chime in)

edit bc i forgot to ping whoops

There don't seem to be any on the market right now so who knows? You can still get the 30 from the Millionaire Center.

The 20 percent one used to be noticeably cheaper on in user shops than the current conversion price for CSC. Many folks would have recomended it or the 10. it takes about six years for me to pay off a 30 percent one. How quickly it might pay back for you depends on how much restocking you do and how much fun you find restocking.

From doing quests alone, I've saved 7m in 2 days from this thing. I'm not big on restocking, but....OMG this is the most worth is CSC purchase that's ever existed. The 20% one is all you need. Restocking is much more frequent than it used to be.