Fibreglass is relatively easy to repair well, if you know what you are doing. I would want to know what caused the crack initially (is it structural, accident, poor workmanship, etc.), and who fixed it (ie. professional or amateur) and how they fixed it. If professional, how long ago, and is there any guarantee/warranty on it.
I would probably also get it surveyed by an independent professional surveyor, giving the surveyor all the information about this situation. And I would also try to get a somewhat reduced price (that may not work if the job was well done, and in fact has made it better than new, but still worth a try).
Let us know how it works out.