Personally I would never use Backpack after reading about people who unknowingly took a package to another country that had drugs and spent years in jail despite their ignorance.
However, if somehow there is a way to do this legally and still capitalize off arbitrage. For example, maybe brands have different MAP pricing in different countries, and even with paying taxes and securing the items, there is a gray market opportunity to exploit.
The simple reality is that this is done on a daily basis already, so finding a way to do it at scale in a legal way has massive potential.
If I was YC, I would consider investing a few bucks to try to tackle this problem knowing that there are hurdles to overcome and some creativity required to make it work.
Travelers won't be able to do this since they won't know the local language, laws and customs, and they won't be licensed importers, and they will be scammed by customs officials in poor countries, and their goods will eventually be forfeited if they don't have enough money to pay the/arbitrary taxes and accrue fees while they decide whether to abandon the merchandise or not.
So yes, the process of importing stuff into many places is shitty and in need of disruption. "Don't get caught, mule" is not that disruption. Customs agents everywhere are united on that and actively looking for people smuggling drugs, animals, produce, electronics, luxury goods and anything else.
Price discrepancies when you factor in transport and taxes are still going to exist and some are going to be opportunities to make small amounts of money, not big amounts.