Choosing an LLM API Vendor: a 6-Point Checklist You Can Test Before Paying (2026)
Teams burned by cheap API resellers know the pattern: degraded models, vanishing vendors, billing black boxes. Six verifications you can run in an hour — model authenticity probes, price-equals-charge, no-fee-on-failure — no trust required.
Why 'cheapest' is usually most expensive
LLM API cost structure is public — upstream prices sit on official sites. A vendor selling below official cost forever can't cover costs; they're either burning subsidy (stops anytime) or substituting the goods (degraded/reverse-engineered/pooled). Integration, migration, and outage costs dwarf the cents saved per million tokens. Buy explainable cheapness, not mysterious cheapness.
The probe: killing the biggest doubt in an hour
Degradation is this industry's trust black hole — you pay for Claude and might get a cheap model in a trench coat. We open-sourced our detector (probe.cocodot.co): six probe families fingerprint the model's actual capabilities, usable against any vendor. Put it in your procurement checklist.
A per-call ledger is table stakes
Finance needs to know where every dollar went. A qualified vendor shows model, token counts, and charge for every call, exportable. A vendor offering only a shrinking balance with no line items can't be reconciled or audited — disqualify immediately.
How we score on our own checklist
Honestly: ① probe is open-source; ② listed prices equal charges, per-call ledger exportable; ③ failed calls never billed; ④ registered overseas company; ⑤ pricing is explainable — no model is priced above its official list, and the discount varies per model (some are clearly cheaper, some match list); check the price page or the models endpoint for current rates rather than assuming one blanket discount; ⑥ our docs list what we don't support: PDF input, no invoices, very high concurrency needs a capacity review upfront, some models carry tiered long-context pricing, and we are a forwarding layer that does not store call content. We learned #6 the hard way — every gap between marketing and implementation eventually becomes a customer incident.
The 6 checks (all pre-payment)
| # | Check | How | Red flag |
|---|---|---|---|
| 1 | Model authenticity | run the open-source probe | refuses testing |
| 2 | Price = charge | 10 calls, reconcile each | no per-call ledger |
| 3 | Fee on failure | force a timeout | failures billed |
| 4 | Traceable entity | check registration, contact support | anonymous payment, TG-only |
| 5 | Sustainable price | compare against official cost | permanently below cost |
| 6 | Honest boundaries | does the doc list unsupported features? | claims everything works |