Dealing with the nightmare client who wants free fixes after a $800 shelf install in north Jersey

So I'm in north Jersey, zone 5 winters making everything a pain, and I just wrapped up installing these heavy-duty IKEA shelves for this lady, quoted her $800 flat rate including the L-brackets and level checks. Everything's solid, but now she's calling every day saying the shelves 'feel wobbly' even though I double-checked the studs with my DeWalt stud finder. Told her it's normal settling, but she wants me to come back gratis to 'reinforce' it with more hardware. Guy in the Handyman Nation Facebook group had a similar rant about picky clients on wall mounts. Tommy Mello talks about setting boundaries in his videos, and yeah, I should've gotten a signed contract upfront. Don't make my mistake, folks, spell out the no-freebies clause clearly. How do you shut down these types without losing the referral?

Screw these entitled homeowners, they think handymen are their personal servants after one job.

Walk away if they push, but document everything with photos before and after. Had a client try to sue over a similar shelf gig, pics saved me.

Ugh, I've dealt with that exact BS on picture hanging jobs. Felt your pain reading this.