Related to your Redywne answer, why aren’t the Redywynes looked down upon for engaging so heavily and directly in commerce? e.g. as Tywin scorns the Pentoshi as “cheeselords” and Sybelle Spicer’s blood is “doubtful” because she has a trader grandfather. Similarly, were such views present in the middle ages, or is it more an attitude of the later aristocracy and idle rich?

Like many aristocrats who got involved in capitalist ventures, the Redwynes are so aristocratic that they can do whatever they want, because no one gets to look down their noses at them. They’re descendants of Gilbert of the Vine and Garth Greenhand, they were Kings in the Time of Heroes, etc. Also, if anyone dares to make an issue of it, they’ve got hundreds of warships and thousands of soldiers to make a point. 

In terms of the historical attitude to “being in trade,” I’ve read some stuff that suggests that attitude came in a bit later when the “price revolution” of the 15th-17th centuries and the “commercial revolution” of the same period greatly enhanced the wealth, power, and independence of the commercial classes while the nobility found themselves handicapped by feudal contracts that limited the rents they could charge their tenants, because the contracts were written in traditional nominal terms that were being eroded by inflation, at the same time that the rise of cities, guilds, and centralizing monarchies were threatening their political power. 

But as with anything else, it’s not consistent. There were plenty of aristocrats who adapted with the changing economy – modernizing agricultural production on their estates, converting cropland into pasturage so that they could get in on the burgeoning cloth trade by producing wool, trying to get rich in the colonies through investment in merchant venture companies, and trying out this newfangled factory system.