The Crimean Khanate was in a strategic position regarding slave trade, and was the center of the Black Sea slave trade. To the North and Northwest they had access to vast areas, to the trade and transport networks, and to the peoples to be captured and traded as slaves. Slave raids extended as far as Poland, Lithuania and Finland.

And to the South they had access to the Ottoman Empire and Middle East which were big markets for slaves. They also had trade access to other khanates in the East, and to Genoa which was a major exporter of slaves to North Africa. It is estimated that between 1200-1760 all in all about 6.5 million slaves were exported through Crimea, most of them women. The economic significance was huge to the slave traders as was the damage to peoples and countries subjected to slave raids.

The slave raiders were often not Crimean Tatars but warlords from places such as Novgorod. Raiders would make raids on villages, capture people as slaves, and sell them forward through the well established trade routes for example by Novgorod -> Moscow -> Dnieper route. Slaves would get sold and bought multiple times on that journey before reaching the big slave markets in Crimea. From there they would get exported to the Ottoman Empire, Middle East, North Africa or other Khanates such as Kazan and Astrakhan.

Let's take for example slave raids to Finland. In the Crimean markets blonde girls and boys captured from Finland and Karelia were most valued because of the color of their skin and hair. And their exceedingly high value made it worthwhile to capture children in the far-away North and to transport them all the way to Crimea to be exported to markets in the Ottoman Empire and Middle East. The slave raids to Finland were most often from Novgorod but there was also raids from Astrakhan khanate.

Here's a relevant paper: The Baltic Finnic People in the Medieval and Pre-Modern Eastern European Slave Trade
Also this blogpost gives context and details with more sources: Blonde cargoes: Finnish children in the slave markets of medieval Crimea

The prices they commanded, however, were simply colossal; one source notes that girls who could be purchased for as little as 5 altyn in Karelia could be resold for 6,666 altyn even before they reached the Khanate – a mark up in excess of 133,000 percent. The higher price, equivalent to 200 roubles or (in about 1600) 250 sheep, was also about five times the usual price for a Crimean slave. It is no surprise, in these circumstances, that slaves from the far north were highly sought-after for their colouring – nor that their special characteristics were scrupulously noted in the slave registers so carefully kept in the ports that lay at the heart of this commerce in human misery: “white skin, white hair.”

There are many factors into a price: rarity, exotism, luxury etc. yet the high prices also tell us these slaves were also valued for their beauty. And the participants on the slave markets had networks for capturing, transporting and trading those blonde slaves from that far.

The clientele knew about these peoples living in the North, sometimes even seeking after them in the markets (for example, Shāh Abbās of Persia sent out delegations to slave markets that seeked after and acquired three Finnish girls in Moscow and 30 more in Kazan), the slave traders knew where to capture them, and raids were extendend as far as the coast of the Gulf of Bothnia in Finland to capture blonde boys and girls.

The slave raids to the North faded over time. But as late as in the 18th century in the Great Northern War (1700–1721) Russia occupied Finland, and unleashed a reign of terror known as the Great Wrath (1713–1721) during which tens of thousands Finns were killed or taken away as slaves.