Grand pianos sometimes need caster cups under the wheels.  They’re easy to install (and cheap to buy e.g. £3 from Ali’s Cave in Tollcross near me in Edinburgh).  Here’s how.

A medium strong person crouches down doggie-style under a corner of the piano near the leg.  Her back is up against the bottom of the piano.  She straightens her arms and legs until the piano goes up high enough for another person to slip in the caster cup.  This won’t hurt her back and impresses the audience especially in the case of a 900 lb. concert grand.  If it does hurt anyone please have her people contact my people for an equitable settlement.

Some customers have annoying neighbours and should consider these expensive items http://www.pianofortesupply.com/accessories/caster-cups/piattino/piattino-acoustic-caster-cups-2/, designed to cut down on transmission of sound along the floor.  -blt