Most likely the problem is not with the plaster repair itself, but with matching the existing texture. Plaster hasn't been commonly used for residential walls and ceilings since the late 1950's and early 1960's. So, that means that whomever textured your ceiling is probably dead and gone by now. Back then, they didn't have texture guns like they do now that simply throw joint compound on the wall or ceiling; they would use various favourite techniques to texture walls and ceilings by hand.
What you'd be best off doing is taking a few pictures of your ceiling texture down to the places listed under "Drywall & Plaster" in your yellow pages. Ask if the texture on your ceiling was commonly used in your area, how it was done, and which of the remaining plastering contractors in your area might still do texturing like that.
There are as many ways to texture a surface as there are plastering contractors, and the biggest problem with any repair to a textured wall or ceiling is usually matching the texture. Most of the time textures are created by smearing or spreading plaster or joint compound on the wall or ceiling in a particular way, but how thin or thick the plaster or joint compound is when it's applied will also affect the end result as well.
If you can see that the ceiling isn't flush with the surrounding ceiling where the repair was done, that's one thing. If you can see cracks around the perimeter of the repaired hole, that's also poor workmanship. However, if the problem is that the texture doesn't match, you really can't blame the contractor too much for that. There are just so many different ways to make texture and so many different variables affecting it's appearance, that it's always difficult to match hand made textures well.
Last edited by Nestor_Kelebay; 04-13-2010 at 04:42 PM.