Oh, so many Thankful statues
They just keep selling them to me! Over and over! And nobody buys them
Shop combo is simply for selling the item on the first go. First its +2 then +8 and then it doubles each time up to +128 exp, where it stays each time. In the second or third time slots, you can easily get two or three +128exp sales, which really pumps the merchant level up.
In adition to this, there's also two pins you can get, one for getting the price very close to the buyers ideal price, which is usually between 100 and 110% markup, which also makes the customer happier, though you can usually go up to 120 or even 130 and get the sale first time, depending if you want more profit or happier customers. There's also a pin for getting the value exactly right, but that's far more luck than judgement.
Also, if you see a heart appear next to someone as you sell to them, it means their relationship has gone up, so they will be able to afford more. So selling only for a small profit will generally make them happier, their pockets will get deeper, and it earns more money in the long run. Apparently.
As for me, I've managed to unlock the third adventurer... and he's going to be rather interesting to level up.
He's the mage, don't remember his name. As you would expect, lots of magic attacks which drink the SP. however, his physical attacks retain sp, 1 for every 10 damage dealt. But his attack is slow, and only hits the square directly in front of him. I'm currently considering if its worth trying to train him up, or stick with Louie since he's never caused me any problems.