Unexpected costs in shipping are the number one reason why people abandon their carts. That's why you need to provide your customers as much information as they need.
Telling your customers at the last minute how long their delivery will take and how much the shipping will cost may lead to a lot of frustration on their part and can eventually hurt your sales.
If you can, try to estimate shipping costs and provide average delivery time early on during the checkout process.
That way, it will be unlikely for your customers to encounter any unpleasant surprises during checkout.
To streamline the shipping process, you might want to tap into a reputable e-commerce fulfillment
service as well.