Try it like this
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:aspnetdbConnectionString %>" SelectCommand="SELECT [mus_ad], [marka], [model], [durum] FROM [servis_kayitlari] WHERE[kullanici_id] LIKE @id">
</asp:SqlDataSource>
in code behind pass your
my_id
value to
@id
parameter like this
SqlDataSource1.SelectParameters.Add("id", DbType.String, my_id );
Hope this works for you :-)