Tricky one! A few parses I'm not entirely sure about, like 10A, but otherwise pretty fair.

Across

1

Leave in observation booth (11)
COMPARTMENT — PART (leave) inside COMMENT (observation)

7

Sprinkling with pronounced cry of relief (3)
FEW — homophone (pronounced) of PHEW (cry of relief)

9

Secretary pinched an expert solution to all problems (7)
PANACEA — AN ACE (expert) inside PA (secretary)

10

Stone added another stone to ten-gallon hat (7)
STETSON — ST (stone), anagram (to) of STONE

11

Shorten any long stuff (5)
NYLON — hidden in aNY LONg

12

Youngster putting on bands and roping in bell-end (9)
STRIPLING — STRIPING (bands) with L (last letter of bell) inside

14

Flying start left a dash or sprint with no hurdles (4,4)
FLAT RACE — F (first letter of flying) L (left) A TRACE (dash)

15

Goddess later divided non-drinkers (6)
ATHENA — THEN (later) inside AA (non-drinkers)

17

Get back in after changing gear (6)
REGAIN — anagram (changing) of GEAR, IN

19

Bridge partners carried off rum top bid (2,6)
NO TRUMPS — anagram (off) of RUM TOP inside NS (bridge partners)

22

Showing or hiding? (9)
SCREENING — double def.

23

Tear up yearbook, except the first of August (5)
ANNUL — ANNUaL (yearbook) without a (first letter of August)

25

Revolutionary following reflected at diplomat's post (7)
ATTACHE — AT TA (reflected), CHE (revolutionary)

27

Small discount, in slightly bad taste (1,3,3)
A BIT OFF — double def.

28

Top lairds went missing every so often (3)
LID — odd letters of LaIrDs

29

Risk premium on greedy man's corruption (6,5)
DANGER MONEY — anagram (corruption) of ON GREEDY MAN

Down

1

Mafia boss and northern bird fattened for the table (5)
CAPON — CAPO (mafia boss) N (northern)

2

Hand run down a folder paper (7)
MANILLA — MAN (hand) ILL (run down) A

3

Gold coin artwork, about just the reverse (2,9)
AU CONTRAIRE — AU (gold), anagram (work) of COIN ART, RE (about)

4

Carry on, say, drawing up scant ensemble (8)
TRANSACT — reversal (up) of ART (drawing) anagram (ensemble) of SCANT

5

Safeguard in case of gentlemen's urethritis (6)
ENSURE — hidden in gentlemENS UREthritis

6

Article mothers take to heart (3)
THE — central letters of moTHErs

7

Celebratory charge covering its upcoming victory (7)
FESTIVE — reversal (upcoming) of ITS, V (victory) inside FEE (charge)

8

Snifter of gin we splashed out on, girl (9)
WINEGLASS — anagram (splashed out) of GIN WE on LASS (girl)

13

Master plan designed to lock one into fatherly care (11)
PATERNALISM — anagram (designed) of MASTER PLAN containing I (one)

14

Every bit beneath wood counter (9)
FORESTALL — FOREST (wood) ALL (every bit)

16

Approximate duration of dietary fibre (8)
ROUGHAGE — ROUGH (approximate) AGE (duration)

18

Extremely glassy and considered spun (7)
GYRATED — GY (outside letters of glassy) RATED (considered)

20

Day in a second rainy season (7)
MONSOON — MON (day) SOON (in a second)

21

Modelling is done from the right or the left (4-2)
SIDE-ON — double def.

24

Cuckoo to fly high in the sky (5)
LOFTY — anagram (cuckoo) of TO FLY

26

Mock recording about love (3)
COD — CD (recording) containing O (love)