Some customers for books in latvian language might be faced to unpleasant postal charges when ordering them from Latvia.
Yes, postage is high,but combining several books together in can become more acceptable. I will use as an example my own postal charges,
As that: Brutto weight (including packing material) up to 100 grams is delivered at  $4, up to 250 grams - $6,
up to 500 grams - $10, up to 1kg - $15, up to 2kg - $30 and so on...
Thsi way practically the higbidder for the book of weight,say 570 grams is waisting other postage up to 430 grams...
Lets compare:
1)Separate delivery of books for 570 grams and 402 grams costs $15+$10 while together 972 grams deliver costs $15 only.
2)Separate delivery of books for 1109 grams,570 grams and 271 grams costs $30+$15+$10 while together 1950 grams deliver costs $30 only.
So it seems to try the chance to combine the postage, and it seems useful to ask the seller how much does the wanted book weight.
An additional tip:
If You buy a book and a postard, You may certainly expect that postcard delivery then is included into book delivery postage...
There might be exceptions, when weight of book does not allow to add 4 grams... or when book format is too small for postcard to put it in... but normally there is no problem about this.
However do not ask to combine together mailing of large and heavy metallic item and a book, it is usually impossible,and may cause the damage of the book.