Answer and anno for 16D left for a rookie commenter till 10 AM.
ACROSS
1 Spooner wagers, he manages somehow (4,2) GETS BY (~bets guy)
4 A group of politicians swallow a crook — like this does! (8) ANACONDA {A}{N{A}{CON}DA} Semi&lit
9 Peace finally — turns out to be otherwise (6) UNREST {p..cE+TURNS}* Semi&lit
10 People in the UK take supplement — it goes to show (8) BRANDISH BR(-it+and)ANDISH
12 He doesn't strike as a poet, carries a weapon (8) SCABBARD {SCAB}{BARD}
13 Encourage operator to take Sunday off (4,2) URGE ONsURGEON
15 Terrible night, in gloom holding two jobs (12) MOONLIGHTING*
18 A long time goes into making things impure (12) ADULTERATION {ADULT}{ERA}{INTO*}
21 Friendly, not changing locations (6) SOCIAL LOCAtIonS*
22 Hamlet's castle relies on trade (8) ELSINORE*
24 Port is left, no way it can be right (8) LARBOARD (-st+l}LARBOARD
25 Oil transformed nation (6) ANOINT*
26 He is no good, always carrying broken idol (8) EVILDOER {EV{IDOL*}ER}
27 Agent gets shelter, wants to lie low (6) SLEEPY {S{LEE}PY}
DOWN
1 Terrible resume, go away (8) GRUESOME*
2 Bull fighter to put one in correct order (8) TOREADOR {TO}{RE{A}DOR*}
3 It's round, it's very hard, understand it's a sporting venue (8,7) BASEBALL DIAMOND {BALL} {DIAMOND} under {BASE}
5 "Managed to raise a thousand", he informs (4) NARK {RAN<=}{K}
6 Business cover taken by citizen face to face (15) CONFRONTATIONAL {CO}{N{FRONT}ATIONAL}
7 Caught as one went to sea, reversed direction initially (6) NAILED (-s+n)NAILED
8 Partners carry two articles, Capital! (6) ATHENS {A}{THE}{NS}
11 Daily breaks record, easy to break (7) FRAGILE {F{RAG}ILE}
14 Tower — metal casing pressurized up to a point (7) STEEPLE {STEE{P}L}{E}
16 Nothing can stop fine extraction from tobacco (8)?I?O?I?E (Addendum - NICOTINE {NIC{O}{TIN}E} - See comments)
17 Descent — maybe can try to get two points (8) ANCESTRY {E}{S} in {CAN+TRY}*
19 I peddled drug, she drank a potion (6) ISOLDE {I}{SOLD}{E}
20 Tax on Peru upsets Puerto Rico (6) OCTROI {puerTO+RICO}*
23 Not against poetry or language (4) ERSEvERSE
GRID
1 Spooner wagers, he manages somehow (4,2) GETS BY (~bets guy)
4 A group of politicians swallow a crook — like this does! (8) ANACONDA {A}{N{A}{CON}DA} Semi&lit
9 Peace finally — turns out to be otherwise (6) UNREST {
10 People in the UK take supplement — it goes to show (8) BRANDISH BR(-it+and)ANDISH
12 He doesn't strike as a poet, carries a weapon (8) SCABBARD {SCAB}{BARD}
13 Encourage operator to take Sunday off (4,2) URGE ON
15 Terrible night, in gloom holding two jobs (12) MOONLIGHTING*
18 A long time goes into making things impure (12) ADULTERATION {ADULT}{ERA}{INTO*}
21 Friendly, not changing locations (6) SOCIAL LOCA
22 Hamlet's castle relies on trade (8) ELSINORE*
24 Port is left, no way it can be right (8) LARBOARD (-st+l}LARBOARD
25 Oil transformed nation (6) ANOINT*
26 He is no good, always carrying broken idol (8) EVILDOER {EV{IDOL*}ER}
27 Agent gets shelter, wants to lie low (6) SLEEPY {S{LEE}PY}
DOWN
1 Terrible resume, go away (8) GRUESOME*
2 Bull fighter to put one in correct order (8) TOREADOR {TO}{RE{A}DOR*}
3 It's round, it's very hard, understand it's a sporting venue (8,7) BASEBALL DIAMOND {BALL} {DIAMOND} under {BASE}
5 "Managed to raise a thousand", he informs (4) NARK {RAN<=}{K}
6 Business cover taken by citizen face to face (15) CONFRONTATIONAL {CO}{N{FRONT}ATIONAL}
7 Caught as one went to sea, reversed direction initially (6) NAILED (-s+n)NAILED
8 Partners carry two articles, Capital! (6) ATHENS {A}{THE}{NS}
11 Daily breaks record, easy to break (7) FRAGILE {F{RAG}ILE}
14 Tower — metal casing pressurized up to a point (7) STEEPLE {STEE{P}L}{E}
16 Nothing can stop fine extraction from tobacco (8)
17 Descent — maybe can try to get two points (8) ANCESTRY {E}{S} in {CAN+TRY}*
19 I peddled drug, she drank a potion (6) ISOLDE {I}{SOLD}{E}
20 Tax on Peru upsets Puerto Rico (6) OCTROI {
23 Not against poetry or language (4) ERSE
GRID