Across:
1 Get a grip on (MASTER) what Margaret Samuels is concealing (what 'margaRET SAMuels' is concealing = retsam) in retrospect (= reverse indicator) (retsam = MASTER),
4 One (I-) culinary tip (‘Culinary’ tip = -C-) good (-G-) in beers (beers), soup (= anagram indicator) (beers = -EBER-S), (ICEBERGS), salads (ICEBERGS),
9 Revenue (Revenue on Line = ROS), turnover (= reverse indicator) (ROS = SOR-) and bank (bank/tier = -ROW) (SORROW) distress (SORROW),
10 Port (P-) to go with Chinese dish (-RICE) that’s served up (= reverse indicator) raw (raw = WAR) (PRICE WAR) – that’ll have the consumers fighting in the shops presumably? (PRICE WAR),
12 The current draw (MAGNETISE) of those following star (Magi) endlessly (i) (‘Magi’ without ‘i’ = MAG-) to pick up (= reverse indicator) 10 (ten = -NET-) tips? It’s so easy! (tips ‘It’s So Easy’ = -ISE) (MAGNETISE),
13 Short (e) article (the) (‘the’ without ‘e’ = TH-) on half of those in 9 across (half of ‘sorROW’ = -ROW) (THROW) from cast (THROW),
14 Posh bloke (TOFF-) taking drugs (-EE) with a number of red brandies (a number of “Red Brandies” = APPLES) (TOFFEE APPLES) and sticky treats (TOFFEE APPLES),
18 Sounds like residencies for The Three Sisters (nursing sisters in NURSING HOMES) and those looking after the welfare of Old Vic, among others (looking after old Vic = NURSING HOMES),
21 Slice of freedom – a hallmark (slice of ‘freedOM – A HAllmark’ = OMAHA) of a part of Nebraska (OMAHA),
22 Pale actor (pale actor) playing (= anagram indicator) (pale actor = CLEOPATRA) old queen (CLEOPATRA),
24 Caught (-C-) between nosy (nosy = SYN-O-) criminal (= anagram indicator) and friend (-PAL) (SYNCOPAL) without making a sound (SYNCOPAL),
25 Knockoffs (COPIES) of firm (CO-) desserts (-PIES) (COPIES),
26 Is under pressure (STRESSED) serving up (= reverse indicator) a number of jelly and ice creams, for example (desserts = STRESSED),
27 Lone star (Lone Star FLAG-) gets to broadcast (-ON) (FLAGON) from vessel synonymous with The Drink (FLAGON).
Down:
1 Dog's dinner (MESS-) – presumably that has to be Pal (-MATE) (MESSMATE), the one that's served at a private function? (army MESSMATE),
2 Take no notice of (SHRUG OFF) indifferent gesture (SHRUG) on holiday (OFF) (SHRUG OFF),
3 Call to mind (EVOKE) First Lady (EV-E) getting to grips with fine (fine = -OK-) (EVOKE),
5 Agreed with (CORRESPONDED) what the men of letters did (CORRESPONDED),
6 M.O. Lar’s (“M.O. Lar’s” = molars = BACK TEETH) sick and tired with these grinders? (sick and tired with these grinders/molars = sick to the BACK TEETH),
7 Ill (= anagram indicator) warder (warder = REWARD) gets compensation (REWARD),
8 Edison leaving out of cowardliness (‘Edison’ leaving out of ‘cowardliness’ = cwarls = SCRAWL) is hard to read (SCRAWL),
11 Cut off (DISASSOCIATE) from detective’s (DI’s = DIS-) sidekick (-ASSOCIATE) (DISASSOCIATE),
15 Almost rue (almost rue) working (= anagram indicator) (almost rue = EMULATORS) with imitators (EMULATORS),
16 Clearing out (EMPTYING) unnatural (= anagram indicator) pigment (pigment = EMPT-ING) around yellowish head (‘Yellowish’ head = -Y-) (EMPTYING),
17 Couple of beastly figures (ass + ass = ASSASS-) up (= reversal indicator) north (NI = -IN) (ASSASSIN) capable of getting away with murder (ASSASSIN),
19 Abolitionists dismiss initial (‘abolitionists’ dismiss ‘initial’ = botoss = BOOSTS) increases (BOOSTS),
20 Employee (EARNER) takes dogs out of rose garden (takes ‘dogs’ out of ‘rose garden’ = rearen = EARNER),
23 Park (P-) war of words (-ROW-) at port (port/left = -L) (PROWL) and go hunting (PROWL).