You can allow the user to remove a previous rating by adding an unrate button.

To add an unrate button subclass the SlickRater or AutoSlickRater class and override the Render method with code similar to the following:

C#
using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using KrispWare;
using System.Web.UI;

namespace localhost
{
    [ToolboxData("<{0}:SlickUnrater runat=server>")]
    public class SlickUnrater : AutoSlickRater
    {
        private const string unrateImg = "/images/unrate.gif";
        private const string unrateImgOver = "/images/unrate_over.gif";

        protected override void Render(HtmlTextWriter writer)
        {
            string escClientID = this.ClientID.Replace("'","\\'").Replace("\"","\\\"");
            string srObj = "slickRaters['" + escClientID + "']";

            writer.AddAttribute("onmouseover",
                String.Format("if ({1}.value > 0) this.src='{0}'; {1}.reset(0)",
                unrateImgOver,srObj));
            writer.AddAttribute("onmouseout",String.Format("this.src='{0}'; {1}.reset()",
                unrateImg,srObj));
            writer.AddAttribute("onclick",String.Format("{0}.click(0)",srObj));
            writer.AddAttribute(HtmlTextWriterAttribute.Src,unrateImg);

            writer.AddAttribute("alt","Click here to remove rating.");
            writer.AddStyleAttribute("cursor","pointer");

            writer.RenderBeginTag(HtmlTextWriterTag.Img);
            base.Render(writer);
        }
    }
}

VB.NET
Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Imports KrispWare
Imports System.Web.UI
 
Namespace localhost
    <ToolboxData("<{0}:SlickUnrater runat=server>")> _ 
    Public Class SlickUnrater
	 Inherits AutoSlickRater
        private const String unrateImg = "/images/unrate.gif"
        private const String unrateImgOver = "/images/unrate_over.gif"
 
        Protected Overrides  Sub Render(ByVal writer As HtmlTextWriter)
            Dim escClientID As String =  Me.ClientID.Replace("'","\\'").Replace("\"","\\\"") 
            Dim srObj As String =  "slickRaters['" + escClientID + "']" 
 
            writer.AddAttribute("onmouseover",
                String.Format("if ({1}.value > 0) this.src='{0}'; {1}.reset(0)",
                unrateImgOver,srObj))
            writer.AddAttribute("onmouseout",String.Format("this.src='{0}'; {1}.reset()",
                unrateImg,srObj))
            writer.AddAttribute("onclick",String.Format("{0}.click(0)",srObj))
            writer.AddAttribute(HtmlTextWriterAttribute.Src,unrateImg)
 
            writer.AddAttribute("alt","Click here to remove rating.")
            writer.AddStyleAttribute("cursor","pointer")
 
            writer.RenderBeginTag(HtmlTextWriterTag.Img)
            MyBase.Render(writer)
        End Sub
    End Class
End Namespace

Note the syntax of the srObj string.

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