ACROSS
1. <nose jobs> RHINOPLASTIES = RELATIONSHIPS*
9. <dour> UNFUN = NUN* outside F U
10. <risk> CRAPSHOOT = CRAP (T after SHOO)
11. <make use of> HARNESS = D out of HARDNESS
12. <build up> ACCRUE = "A CREW"
14/19. SEMINARS* = NEAR MISS <not quite a hit?>
15. <played a role> DID ONE'S BIT = DIDO + NESBIT
18. <having issue> FATHERHOOD = HEARTH* inside FOOD
22. I'M PE D_E = IMPEDE <bar>
24. ←(...s)TASY BAB(b...)← = BABYSAT <relieved parents>
26. T RUN D outside STFU = TRUST FUND <financial store?>
27. AG + OR A_ = AGORA <marketplace>
28. LACKEY inside (EP BASED)* = BLACK-EYED PEAS <rap group>

DOWN
1. G H inside ROUEN = ROUGHEN <feel coarser>
2. <narc> INFORMANT = (IN FOR) MAN _T
3. _O_ INKED = OINKED <behaved like a pig?>
4. LOCKS MIT H_ S_ = LOCKSMITHS <key workers?>
5/25. SLUNK outside DAM* = SLAM DUNK <open-and-shut case>
6. <covertly> IN SECRET = INSECT outside _R _E
7. SCOUR = SCOUSER - S_E
8. (...u)STRE ET(c...) = STREET <the Royal Mile, perhaps>
13. (BOYS DO DUMB)* = BOSOM BUDDY <close friend>
16. <sulphurous rock> BRIMSTONE = BRIMS + TONE
17. <quarrel> VENDETTA = E_N inside (V + "DEBTOR")
18. <coquettish> FLIRTY = FLY outside I R_T
20. ←SPARTA'S← = SATRAPS <Persian governors>
21. AD outside B_ OAR = ABOARD <on ship>
23. <sound> PLUMB = PLUM B