Toby - it is usual to cut rosewood and then leave it to season before making furniture from it, then cracks are never a problem. Some makers do varnish, others just stain and polish the wood, either is OK.
Unfortunately some characters make furniture with green wood which has not dried properly - this can be prone to cracking. Others even worse, take cheap wood and stain it to look like rosewood - you can normally tell this from the heavier grain.
If the wood itself has cracked you can buy wood repair putties from Home-fix in various wood colours if you feel you have the ability to repair it and possibly stain and polish or varnish it yourself. If not you are better going to a reputable rosewood manufacturer such as Singapore Woodcraft to get a quote to refurbish for you.