Not a lot to say about this one. One minor quibble (16a), a few neat clues but nothing that really stands out.
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Across
1 INCOME IN (popular) CO (firm) M[assiv]E
4 TRAGIC *(TRACI[n]G)
8 DEANERY *(YEARNED)
9 ACQUIRE homophone of ‘a choir’
11 BLOODY MARY *(BY OLD MAYOR)
12 MINT hidden in ‘calM INTellectual’
13 BREED RE (about) in BED – ‘about to enjoy retirement’ = ‘in bed’
14 LIPSTICK LIP (backchat) STICK (criticism)
16 DIPLOMAT DIP (creamy mixture) MA (master) in LOT (crowd) – MA is the abbreviation for ‘Master of Arts’ not simply ‘master’
18 ARGUE R[egatta] in AGUE (fit)
20 VAIN homophone of ‘vein’ (humour)
21 GROGGINESS GROG GIN (drinks) [m]ESS (dining area)
23 CROESUS *(COURSES) – the king of Lydia renowned for his wealth
24 SOJOURN JOUR (day, in French) in SON (child)
25 CUTLET CUT (economy) LET (allowed)
26 SPRAIN [tou]R in SPAIN (country)
Down
1 IDEAL I DEAL (admission by trader)
2 CONDONE DON (river) in CONE (solid figure)
3 MARTYRDOM ARTY (creative) in MR (gentleman) D (degree) OM (honour)
5 ROCKY cd
6 GOURMET GOUR[d] (a lot of fruit) MET (satisfied)
7 CHRONICLE CHRONIC (deplorable) LE (article written by Hugo)
10 BALLOT BOX cd
13 BRIC-A-BRAC hidden in ‘ruBRIC ABRACcadabra’
15 PLAYGROUP P (piano) LAY (song) GROUP (set)
17 LENIENT *(LINE) ENT (part of hospital)
19 GONDOLA N (new) DO (complete) in A LOG (a record) reversed
21 GAUZE U (university) in GAZE (look)
22 SIREN RE (engineers) in SIN (error)
23a took me back by many years. In the late Sixties Panther Books published a series of Croesus Book of Crosswords – these previously unpublished puzzles were by an anonymous compiler. I liked them.