Your bike has cartridge bearings, which are replaceable, usually by buying a new bottom bracket. (I don't have experience with the older loose ball bottom brackets.)

If I suspect my bearings are getting rough, I'll take the chain off the crank (I use quick links to join the chain, so it's easy.) Then spin the crank without the chain to see that it spins fairly freely (it won't spin a long time like a wheel does).

If I then suspect worn bearings, I'll pull the crank off and use my fingers to turn each side's bearings by hand. I can feel if one or both are rough.

(Your mechanic can tell when it's "1000 km" from needing replacement? Huh.)