What if a Tron energy seller only sells fixed packs?

Short answer

Some sellers will not delegate 65,000. They delegate a pack. If you allow it, a Tron energy rental can come back larger than you asked, and it will not come back smaller. The larger pack is kept only when it costs less than burning the energy you actually wanted. If your books need the exact number, say so, and every other pack is ignored.

You asked for 65,000 and the answer said something else

The first time this happens it looks like a bug. You typed 65,000, the response says 100,000, or some other round shelf size. The addition is fine. That seller does not split the pack.

The extra energy is real. It shows up on your address and you can spend it before the rental ends. You also pay for it. The guardrail is a comparison with burning. If the pack costs more than the TRX the network would have destroyed for the amount you asked for, the pack is thrown out and a closer offer is used. If every offer is a bad pack, you get no price. A missing price is a better outcome than a bill padded past the point where renting made sense.

Turn the exact option on when a payout script assumes the delegation is 65,000 and will mis-count anything else. You then get 65,000, or you get nothing from the sellers who only stock other sizes. Nothing in that mode upgrades you quietly. The price you are shown is still the lowest offer that survived this test, not the lowest number a seller shouted.

The burn ceiling uses your request, not the pack

By default, a returned volume may be higher than the request and is never lower. Set exact_volume and a seller who cannot delegate that integer is skipped.

The ceiling is the burn of the requested energy, before any activation fee: requested energy, times the chain's sun price, divided by 1,000,000. Above that, the pack is dropped. Equal to it, the pack stays. You are not worse off than doing nothing. At the 100-sun snapshot, a request for 65,000 burns 6.500000 TRX, and that is the ceiling a substitute has to fit under. The transfer only spends 64,285, which would burn 6.428500 TRX, but you cannot request 64,285. The minimum is 65,000, so the ceiling you actually get is the burn of 65,000.

A longer duration follows the same idea when you have not demanded an exact duration. The substitute may last longer. It may not last less time. And it has to fit under the burn of the energy you requested. Activation, if the address needs it, is added after that comparison. It is not an excuse to keep an expensive pack.

Say the ceiling on a 65,000 request is 6.5 TRX. A 240,000 pack at 7 TRX is dropped. The same pack at 4 TRX is kept. The same pack at 6.5 TRX is kept. Those are shapes, not a live quote. The 240,000 does not change what one transfer consumes. The transfer still spends 64,285 or 130,285. The rest sits there until the clock ends or until later transfers use it. On a 15-minute rental, refill will not turn a modest leftover into another planned transfer. The leftover has to be at least 64,285 on its own. How many transfers a pile covers is the count to use on whatever volume came back.

If every seller misses the exact size, or every larger pack fails the burn test, there is no invented price. An order so large that no seller can approach it in one fill is refused. From code, both flags are on the energy rental API. Leave them off and you are saying a better-priced larger fill is welcome.