Hard! Half the clues went in pretty easily, then a little flurry of mostly-sure answers which gave me enough letters to struggle through the final stretch. Being forced to actually work out the wordplay was a good exercise.

Across

1

Hearing aid to leave back on shelf if pinched? (7)
BAILIFF — BAIL (to leave) F (back on shelf) surrounding (pinched) IF

5

King's ransom squared away? (4,3)
TIDY SUM — &lit, cryptic def.

9

Friday partly free (3)
RID — hidden (partly) in fRIDay

10

Old PM in loud shades, acquiring pot (5,6)
BILLY HUGHES — homophone (loud) of HUES (shades) after BILLY (pot)

11

Squat once refurbished into Canberra museum (9)
QUESTACON — anagram (refurbished) of SQUAT ONCE

12

Unwrapped whip and switch say - a device for swingers? (5)
HINGE — wHIp aNd (unwrapped), reversal (switch) of EG (say)

13

Even keenly concealing delicacy on request (8)
ENTREATY — ENY (even letters of keenly) outside (concealing) TREAT (delicacy)

15

Paranormal sleuth has row with spy base (6)
SCULLY — SCULL (row) Y (last letter of spy)

19

(& 18-across) Koalas adorning rocky koala sanctuary (8,6)
KANGAROO ISLAND — anagram (rocky) of KOALAS ADORNING

22

Prize name of lover-boy? (5)
CUPID — CUP (prize) ID (name)

24

Stunning blue Fiat convertible hugging bend (9)
BEAUTIFUL — anagram (convertible) of BLUE FIAT with U (bend)

26

Excel in jams, removing plugs from headset? (11)
SPREADSHEET — SPREADS (jams) HEadsET (removing central letters)

27

DeLillo regularly cut back fiction (3)
LIE — reversal (back) of EIL (even letters of delillo)

28

Crass scam also exposed villains (7)
RASCALS — cRASs sCAm aLSo (exposed)

29

Lair providing grisly details, at wit’s end (7)
HIDEOUT — HIDEOUs (grisly without last letter; details) T (last letter of wit)

Down

1

Hole pierces sailing ship - fancy! (7)
BAROQUE — O (hole) inside BARQUE (sailing ship)

2

Vin Diesel shot art film… (5)
INDIE — hidden (shot) in vIN DIEsel

3

…with precious lines, popular Affleck, at the heart? (2,7)
IN BETWEEN — TWEE (precious) inside (lines) IN (popular) BEN (Affleck)

4

Bliss novel - life on the edges? Carey nails it! (8)
FELICITY — anagram (novel) of LIFE on IT inside CY (edges of carey)

5

Flirting love integral to coupling (6)
TOYING — O (love) inside (integral to) TYING (coupling)

6

Stuff of bagels and big bickies? (5)
DOUGH — double def.

7

Swimming children’s lifesaver (9)
SCHINDLER — anagram (swimming) of CHILDREN'S

8

Set snarls, really extreme, linked to DA's puzzle (7)
MYSTERY — anagram (snarls) of SET, then RY (extreme letters of really) after MY (linked to DA)

14

Said to count skimmed accounts to make rapid transfers? (9)
TELEPORTS — homophone (said) of TELL, rEPORTS (accounts without first letter; skimmed)

16

Thought company upset on losing principal (9)
COGITATED — CO (company) aGITATED (upset without first letter)

17

Lord's town in New Zealand - Haast down south - rebuilt on bores (8)
NAZARETH — anagram (rebuilt) of NZ (New Zealand) HAAsT without (down) s (south), with RE (on) inside (bores)

18

Favoured vocal one measuring tooth (7)
INCISOR — IN (favoured), homophone (vocal) of SIZER (one measuring)

20

Slickest Love Island 27-across linked to do-gooder (7)
OILIEST — O (love) I (island) LIE (27-across) ST (do-gooder, saint)

21

One with tendencies to doff a pair of waders? (6)
IBISES — I (one) BIaSES (tendencies) without (to doff) a

23

Play old woman with 'arsh upbringing (5)
DRAMA — MA (old woman) after reversal (upbringing) of ARD ('arsh)

25

Leaf of forest elm will colour in seconds (5)
FOLIO — second letters in oF fOrest eLm wIll cOlour