Watch old boy attend to customers (7)
I believe the answer is:
observe
'watch old' is the definition.
'observe' can be an answer for 'watch' (observing is a kind of watching). I'm unsure of the 'old' bit.
'attend to customers' is the wordplay.
'attend' becomes 'serve' (synonyms).
'to' says to put letters next to each other (I've seen this in other clues).
'customers' becomes 'ob' (I can't explain this - if you can you should give a lot more credence to this answer).
'serve' after 'ob' is 'OBSERVE'.
'boy' acts as a link.
Can you help me to learn more?
(Other definitions for observe that I've seen before include "Notice, watch" , "Watch attentively" , "Espy" , "See - keep - remark - maintain - celebrate" , "Discern" .)