querying multiple values from one column
SELECT 
DESCRIPTION,
item,
cust_code,
pack_description,
uos,
pack,
total_value,
total_value_vat,
total_value_goods,
price_indicator
from TRANSACTION_DETAILS
where cust_code=1273 
and item in
(
    371355,
    371476,
    371629,
    370556,
    370677,
    370820,
    370952,
    371070,
    371223,
    372154,
    372253,
    371751,
    371872
)


As for duplicates, you're going to have to decide how you want duplicates handled.  Using a GROUP BY, if there is a duplicate item you will have to figure out how to aggregate the rest of the data for the result set.  Feel free to give me that info and I can write up your aggregate query.