Shipping & Handling Charges should be very close to actual Shipping Charges only + no more than $1 or $2 for Handling.
In many cases I have included estimates for Shipping & Handling Charges for the convenience of quick and easy check out.
When I prepare your item(s) for shipping, if I discover the S&H charges you have paid are more than $2 more than actual shipping charges - I will refund you the difference. (If the S&H charges are less than actual shipping charges, I will accept that loss and you will NOT be billed the difference.
Or if you prefer to contact me prior to checkout, I can calculate the actual S&H charges and you can pay the correct amount upon check out.