Charge less to end user getting fifty litres (9)

I believe the answer is:

undersell

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'charge' is the definition.
The definition and answer can be both to do with ownership as well as being verbs in their base form.
Maybe you can see a link between them that I can't see?

'less to end user getting fifty litres' is the wordplay.
'less' becomes 'under' (I've seen this in other clues).
'to end user getting' becomes 'se' (I am not sure about this - if you are sure you should believe this answer much more).
'fifty' becomes 'L' (Roman numeral).
'litres' becomes 'L' (abbreviation).
'under'+'se'+'l'+'l'='UNDERSELL'

Can you help me to learn more?

(Another definition for undersell that I've seen is " Insufficiently promote (something)".)

I've seen this clue in The Irish Times.

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