ACROSS1 Pass market that has one pound off oil (6) DIE,SEL(l)
4 I say that woman's involved in survey on energy (4,4) LOOK HERE - HER inside LOOK and E
5 Corporation strike over unlimited pay (6) PAUNCH - (p)A(y) inside PUNCH
9 Money-making drama pilot bore trashed (9) POT-BOILER - (pilot bore)*
10 Hand bound to land with flipping force on son (4) SERF - 'hand bound to (the lord's) land' (as they were in the feudal system) - S(on) followed by F(orce) + RE (on) all rev.
11 Fish seen around river channel (6) TRENCH - R inside TENCH
12 Criminal is catty about husbands celibacy (8) CHASTITY - H inside (is catty)*
14 It is real nasty (8) LISTERIA - (is real)* 'It' is not an adequate 'definition' for this answer.
16 I managed land (4) I,RAN
18 Honour God's will, so they tell us (4) FETE - homophone for 'fate' - hard to spot; first of two possible blasphemities
19 Quantities of game (8) DRAUGHTS - dd
21 If I must steal, a thankyou’s required first (2,1,5) AT A PINCH - A TA + PINCH
22 Upset singer regularly ignored Latvian icon (6) AVATAR - a RAT is a 'singer' - as he informs on someone in this case + alternate letters of 'Latvian' - all rev.
24 Mark Rothko’s first piece after unfinished study (4) SCAR - SCA(n) + R(othko)
26 Say what you want to say about wit hitting guards (3,4,2) OUT WITH IT - OUT (about) + WIT + HIT(ting) - or something like that
27 Figure you must visit New York? (6) STATUE - U for 'you' inside STATE for 'New York' - it has a question mark, because it is questionable; or at least a weak clue
28 Posh people experiment with dope (6) GENTRY - GEN is 'dope' and TRY is 'experiment'
DOWN
2 Saucy material that one male suppresses (11) IMPERTINENT - I + M + PERTINENT
3 Protest Congress blocking Pride? (3-2) SIT-IN - IT (sex = congress) inside SIN - again the question mark is needed, because this is what is is called DBE: definition by example; another poor clue
5 District making soprano a persona non grata (6) PARIAH - PARIsH changing the S to A
6 Distressing way to increase crossword output? (9) UP,SETTING
7 My sort of music comes up short (3) COR - Cor! and My! are equivalent exclamations - ROC(k) rev.
8 Chess players not allowing any middle ground (5-3-5) BLACK-AND-WHITE - dd
13 One brought in to take lead in Cheers? (11) TOASTMASTER - this is a cryptic definition (Cheers is a TV show if you didn't know)
15 God? Time His tripe must be thrown out! (3,6) THE SPIRIT - "God' is a poor synonym for THE SPIRIT, imo; T + (his tripe)*; sounds blasphemous, btw; lucky this is not published in the 'land I managed'
17 A big band playing without any difficulties (4-4) BADA-BING - I believe I might have heard this expression; (a big band)* - this anagram took me a while
20 Returns home with company and yours truly (6) INCOME - 'home' is usually IN + CO + ME ('yours truly' - cant phrase for 'me')
23 When stag's other half drained of colour (5) ASHEN - AS = 'when' + HEN - the equivalent of 'stag' in single-gender parties before weddings
25 Dude in Bombay? (3) CAT - slang for 'bloke' + a type of feline