A used IBC tote is not a complicated object. It is a bottle, a cage, a pallet and a few fittings. A quick walk-around tells you most of what you need to know, whether you are looking at a single tote at a farm sale or a truckload from a supplier.
Step 1: Walk the bottle
Walk a slow circle and look at the bottle through the cage. Look for staining or discoloration from prior contents and for any visible bulge or flat spot. A bottle that bulges at one corner may have held a heavy or aggressive liquid.
Step 2: Check the cage geometry
Forklift damage shows. Verticals will be off-plumb or a horizontal bar will be bent. Minor cosmetic dents are common and usually fine. Major distortion at the corners suggests the bottle inside may also be deformed, and is a reason to pass.
Step 3: Cycle the valve
Open and close the discharge valve a couple of times. A healthy valve turns with even resistance both ways. A gritty valve, or one that sticks at the end of its travel, is worn. That is not a disqualifier, but if you are buying as-is, plan on a replacement.
Step 4: Look inside the fill cap
Open the fill cap and look inside with a flashlight. Check for residue, film or discoloration on the walls and floor. Do not lean in to sniff: if you do not know what the tote held, treat any residue as potentially hazardous. A strong or lingering odor is a reason to keep that tote away from anything food-related.
Step 5: Look under the pallet
Confirm the pallet is intact, with no cracked boards or stringers on wood and no shattered corners on plastic. A pallet that fails in transport is one of the few things that can ruin a tote outright.
Step 6: Ask for the paperwork
Ask what the tote held last, and ask for it in writing. If the seller cannot say, the tote may still suit non-contact storage or repurposing, but it should not go into food service, and it should not be priced as if it could.
That is the whole check: bottle, cage, valve, interior, pallet, paperwork. It will not replace a proper reconditioning process, but it will catch the obvious problems before you buy.