How is a particular used book selling and how much is it around the world?

Over at BookFairs.Com, several book search engines are talked about, including viaLibri.

viaLibri, which has been recently redesigned, has an advanced search form that has many options.  It claims to be the world's largest search engine for old, rare & second-hand books, including searching international booksellers.

It's our go-to to get a sense of the market for scarcer material, especially when there's just too much "noise" on the individual marketplaces.

(https://www.bookfairs.com/book-search.html)

You can search for many books that are outside the US all at the same time

 Books for sale from outside the US that are new, used and textbooks can be searched at AddALL.  They offer many search features, including displaying currencies in search results.

(https://addall.com/)

Do quick book searches using an ISBN

 Bookfinder, a book shopper's search engine, has on its search form a box for the ISBN.  The ISBN, to be found on many books' copyright pages (especially in newer books), is a book identifier number booksellers use.  It can also be found on the book's back cover; it comes in both 10- and 13-digit lengths.

The ISBN can be used by itself on Bookfinder's search form; and, most other book shopping sites have the feature.

(https://www.bookfinder.com/)