Arbitrage
is the buying and selling of assets (usually financial instruments) by taking advantage of price differences in different markets. This is as common as pigeons.
I don't have any problem with intermediate vendors doing this, as their influence isn't the primary driver of market prices. Unless they come to dominate a very small local market, in which case they can drive up prices.
In my local (large) market, there are dozens and dozens of bikes available at relatively cheap prices. More than anyone could ever want or need. Very few are in fully refurbished, cleanly presented, truly ready-to-ride condition. This type of bike commands a premium price...and gets it.