Depending on what type of strings you are processing, and what types of information you are "scraping:" you might use different strategies.
If you want only numbers, write a RegEx that removes everything but numbers. Something like:
YourString = Regex.Replace(YourString, "[^0-9.]", "");
In the case of your example : "+9%" : only the percent sign needs to be removed to get a valid integer:
private int i;
private bool IsNumber;
private string n = "+9%";
private void SomeMethod(string testString)
{
n = n.TrimEnd('%');
IsNumber = Int32.TryParse(n, out i);
if (IsNumber)
{
}
}