The most common reason for an abandoned cart is not doubt about the product. It is a number the customer did not expect, revealed at the moment they were ready to pay. Shipping is a price. Treat it as one and show it where the other price is.
On the product page, next to the price
Delivery cost and delivery time, in one line under the price: "£3.95, arrives in two to three days." If shipping is free above a threshold, say the threshold there too. Nobody should learn what it costs to receive the product after they have decided to buy it.
Shipping is a price. Show it where the other price is.
In the cart, as a bar
If you offer free shipping above a spend, show a bar with the distance to it. It is the one piece of cart design that reliably raises order value, and it works because it is honest: the customer can see the deal and decide.
Returns in one sentence
"Free returns within thirty days." "Exchanges only on sale items." Whatever the policy is, it belongs in a sentence on every product page, not a link to a page of terms. The absence of the sentence is read as bad news.
Where you ship from, and to
A line in the footer and on the product page: where you are, which countries you deliver to, and roughly how long it takes. International customers will not guess. They will leave.
Do not hide it in the checkout to protect conversion
It does not protect conversion. It moves the exit to the last step, where it costs you a customer who had already said yes. Say it early, lose the people who were never going to pay it, and keep the ones who were.
Tell people the shipping cost first and they stop leaving at the end.
