Across:
1 It’s just about (ALMOST) old master with no red (‘old master’ has no ‘red’ = olmast = ALMOST),
4 Pity an (pity an = -YPTIAN) oddball (= anagram indicator) following (= positional indicator), for example (e.g. = EG-) (EGYPTIAN), one of those in Africa (EGYPTIAN),
9 For example, Henry (-KING) the Sixth (VI-), from the start (= position indicator) (VIKING), was one of the early invaders of Ireland (VIKING),
10 Discover (discover = DIVORCES) all over the place (= anagram indicator) how marriages end (DIVORCES),
12 How does Carol (SING) connect with American (A) dance partner? (SONG and dance) (SING A SONG) Twitter! (SING A SONG),
13 Is critical (VITAL) of Victoria (V-), Ita (-ITA-) and April at The Foundation (‘April’ at the foundation = -L) (VITAL),
14 It’s not (not = NO -T) about 23 down (‘doubt’ = DOUBT) finding answer (A-)? Everyone (ALL) (NO DOUBT AT ALL) is definitely sure about that! (NO DOUBT AT ALL),
18 Someone with a job picking up nails (“tacks collector” = “TAX COLLECTOR”) reported (= homophone indicator) to Revenue (TAX COLLECTOR),
21 For instance, Chardonnay (wine) starting to go off (w) (‘wine’ without ‘w’ = INE-) with port (-P-) and top Tawny (top ‘tawny’ = -T) (INEPT) is not up to scratch (INEPT),
22 Together with (-AND) nude (nude = DUNE-) model (= anagram indicator) in Titanic, for example (S- -S) (SAND DUNES), and On the Waterfront (SAND DUNES),
24 College (-C-) in Orient (Orient = INTER-O-) sabotaged (= anagram indicator) by mass (-M) (INTERCOM) communications system (INTERCOM),
25 Leaders of an unusual political alliance, in reality (leaders of ‘an unusual political alliance, in reality’ = AU PAIR), a proponent of the nanny state perhaps (AU PAIR),
26 Cool (UP-TO-DATE) model’s (= anagram indicator) pout (pout = UP-TO-) is for potential partner (-DATE) (UP-TO-DATE),
27 Serves up (= reversal indicator), for example (e.g. = -GE), Dorothy’s (Dots = STOD-) (STODGE) heavy food (STODGE).
Down:
1 Giving one the heads up (ADVISING) streaming video without remote (‘streaming video’ without ‘remote’ = saingvid = ADVISING),
2 Coping (MAKING DO) with board member (chessboard member = -KING-) in senseless (MA-D-) order (-O) (MAKING DO),
3 Travels everywhere return on one day (SANTA) with dancer’s boss (SANTA is reindeer Dancer’s boss),
5 Is Independent (GOING IT ALONE) doing a solo run? (GOING IT ALONE),
6 It’s not worth it (POOR VALUE) to back (= reversal indicator) Trim (t) group (‘troop’ without ‘t’ = POOR) at benefit (VALUE) (POOR VALUE),
7 Dietician gets rid of aid (‘dietician’ gets rid of ‘aid’ = ieticn = INCITE) to stir up trouble (INCITE),
8 Is only (is only = NOSILY) strange (= anagram indicator) in a curious way (NOSILY),
11 A gent’s associate (agent’s associate / spy’s associate = CONTACT) is fishing (SPORT) (CONTACT SPORT) for one of those handy types in Ring (CONTACT SPORT),
15 Learn duet (learn duet = UNALTERED) arrangement (= anagram indicator) as is (UNALTERED),
16 Relative (-DA-) is right (-R-) in part of the stadium (STAN-D) (STANDARD) for The Banner (the banner/flag = STANDARD),
17 Keep (PRESERVE) page (P-) from book (-RESERVE) (PRESERVE),
19 Son gets out of limousine (‘son’ gets out of ‘limousine’ = limuie = MILIEU) in cultural surroundings (MILIEU),
20 Get lost (BEAT IT) in Tibet? A (Tibet a = BEAT IT) mistake! (= anagram indicator),
23 Lack of confidence (DOUBT) in Irishman (D-UB-) around old (-O-) square (-T square) (DOUBT).