Do Kumos quests ask everybody for the same items? Is this why we are seeing common items at overinflated prices? If it is is something being done? If it isn't then what is going wrong?

It might be the quests in some cases, but in the case of this particular item, I believe it's users buying them up and deliberately inflating the price. This has happened with items bought from my shop for normal prices and then put in these same other shops for the ~50mil prices, same as the bongos.

I must admit this is an extreme example. Mostly I see things inflated to around the 40k mark.

[edit] here's a better example:

Shop Search results for Murders 101 Shop Price Amount Buy User Shops //// 58,000 sP 3 //// 58,000 sP 1 //// 58,000 sP 1

also might have to do with the fact some common/normal rarity items just are not restocking at all in the main shops.