Ok I am interested in a guitar online but it had a cracked top the owner said it has been repaired but my question is how will that effect the sound? it has a gloss finish and am not sure if the crack went all of the way through. Thanks for your help!!
Chances are, if the top cracked, it went all the way through - they usually do. The reason a top cracks is usually do to a lack of humidity. The humidity drops in the Winter, then rises in the Spring and Summer. After a couple of these cycles, the top splits.

If the repair job was professionally done, you won't be able to hear the difference. If you decide to buy it, invest in a small room humidifier and keep the relative humidity somewhere between 40% and 50%. Unless you live in a place where the humidity is good all year round.
My guitar has a crack in the top (from playing very percussive music), and I really can't hear the difference. The soundboard of a guitar is usually pretty thin, and under a lot of tension which is how the sound is produced, but I honestly can't see it affecting the tone that much, if its a small crack, and the top still vibrates as one.
I think most cracks on the top of guitars don't effect the sound. If it's cheap and the cracks not bad, I would definitely consider the guitar. I had some issues with humidity earlier, but I put my guitar in it's case with a couple sponges and it "healed". I don't think you would need a humidifier if you use a case and use the "sponge method".
I'd never buy a guitar that had a crack in the soundboard. The back or sides ... well, maybe if it was a vintage instrument I really wanted, but not otherwise.

It would have to be a really, really, really good deal for me to even consider something like that.
Sincerely, Chad.
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