Dreamweaver SQL returning extra results

I'm having a problem with my database search query. It comes from a form asking either title, author or isbn - requesting a title returns perfection, requesting an author or isbn returns the correct result, plus 2 seemingly random results - but the same 2 odd results every time for every query.

Thanks

Dim SearchQuery__MMColParam
SearchQuery__MMColParam = "1"
If (Request.Form("title") <> "") Then
SearchQuery__MMColParam = Request.Form("title")
End If
%>
<%
Dim SearchQuery__MMColParam2
SearchQuery__MMColParam2 = "1"
If (Request.Form("author") <> "") Then
SearchQuery__MMColParam2 = Request.Form("author")
End If
%>
<%
Dim SearchQuery__MMColParam3
SearchQuery__MMColParam3 = "0"
If (Request.Form("isbn") <> "") Then
SearchQuery__MMColParam3 = Request.Form("isbn")
End If
%>

<%
Dim SearchQuery
Dim SearchQuery_cmd
Dim SearchQuery_numRows

Set SearchQuery_cmd = Server.CreateObject ("ADODB.Command")
SearchQuery_cmd.ActiveConnection = MM_conn_STRING
SearchQuery_cmd.CommandText = "SELECT * FROM Stock WHERE title LIKE ? OR author_last LIKE ? OR isbn=?"
SearchQuery_cmd.Prepared = true
SearchQuery_cmd.Parameters.Append SearchQuery_cmd.CreateParameter("param1", 200, 1, 255, "%" + SearchQuery__MMColParam + "%") ' adVarChar
SearchQuery_cmd.Parameters.Append SearchQuery_cmd.CreateParameter("param2", 200, 1, 255, "%" + SearchQuery__MMColParam2 + "%") ' adVarChar
SearchQuery_cmd.Parameters.Append SearchQuery_cmd.CreateParameter("param3", 5, 1, -1, SearchQuery__MMColParam3) ' adDouble

Set SearchQuery = SearchQuery_cmd.Execute
SearchQuery_numRows = 0
%>

you have the default values for the recordset parameters set to 1 and 0, try changing those to -1 for all of them.