A little bit imprecise, and I wasn't too thrilled with 26A. I don't know if it's a straight error, but port is the left side. I took the more generous interpretation that "rail" is to the right of port, but given the level of the rest of the clues, I don't really think that fits with RM's setting. Anyway, a pretty easy cruise if you don't look too hard!

Across

1

Though all bet, its backers lost (6)
ALBEIT — ALl BEt ITs, each without last letter

4

Legal support for the devil is to be inferred (8)
IMPLICIT — IMP (the devil) LICIT (legal)

10

Communicate need to reach the other side (3,6)
GET ACROSS — double def., cryptic def.

11

Run into Dick who is heartless and legless (5)
DRUNK — RUN in DK (dick without middle letters)

12

Too wary of lovers' skinned fishy (14)
OVERSUSPICIOUS — OVER (lovers without outside letters) SUSPICIOUS (fishy)

14

She who loathes has a broken heart (5)
HATER — anagram (broken) of HEART

16

Dancer has a jolly good time with Erina (9)
BALLERINA — BALL (a jolly good time) ERINA

18

Such speed is dangerous, have a rest and cuddle (9)
BREAKNECK — BREAK (rest) NECK (cuddle)

20

Chocolate substitute makes cobra sick (5)
CAROB — anagram (sick) of COBRA

21

He carries the flag for a common-or-garden beam (8-6)
STANDARD-BEARER — STANDARD (common-or-garden) BEARER (beam)

25

Plant louse can help to contain acid level (5)
APHID — AID (help) around PH (acid level)

26

Depiction of rail on the right, say (9)
PORTRAYAL — homophone (say) of RAIL to the right of PORT (left)?

27

Ram meant to blow up military equipment (8)
ARMAMENT — anagram (to blow up) of RAM MEANT

28

Seem to be a very quiet listener (6)
APPEAR — A PP (very quiet) EAR (listener)

Down

1

She hates English 'Oblong Heap' buildings (10)
ANGLOPHOBE — anagram (buildings) of OBLONG HEAP

2

Wash the baby's tops first (5)
BATHE — BA (first two letters of baby) THE

3

Romanticise extracting mate's rotten tooth (7)
INCISOR — anagram (rotten) of ROmaNtICISe without MATE

5

Some Kenyans like mum's AI (5)
MASAI — MA'S (mum's) AI

6

Anti-tech bishop and I are into the lute (7)
LUDDITE — DD (bishop) I inside LUTE

7

Courier wraps a little tutu for the fashionista (9)
COUTURIER — COURIER around UTU (tutu without first letter)

8

Have a point of view on gross profit (4)
TAKE — double def.

9

Take possum bible on vacation? It's feasible (8)
POSSIBLE — POSSum bIBLE without middle letters

13

Thief who goes up the wall after Tom? (3,7)
CAT BURGLAR — CAT (tom) BURGLAR (thief), &lit

15

(& 17-down) Be contemptuous, turn them over and fertilise? (5,4,4,4)
TREAT THEM LIKE DIRT — cryptic def.

19

Realm where mink and dog cavort (7)
KINGDOM — anagram (cavort) of MINK DOG

20

Brighten her puce ensemble (5,2)
CHEER UP — anagram (ensemble) of HER PUCE

22

While writer is a tree (5)
ASPEN — AS (while) PEN (writer)

23

Even men may charm and reply in verse (5)
RHYME — reversal (reply) of EMYHR (even letters of men may charm)

24

Heads back to an avalanche of molten rock (4)
LAVA — reversal (back) of AVAL (first letters of avalanche)