Tell a known fault from an unknown condition
An item with a described fault and an untested item are not the same offer. In the first case at least one problem is known; in the second, whether it works is still unknown. In neither case can you assume the problem will be simple and cheap. On Izsoli.lv such lots are marked with the condition «For parts» or «Untested».
«Won't power on» is a symptom, not a diagnosis. The cause may be the power supply, the electronics or another part. Tell a seller's guess apart from a conclusion confirmed by diagnosis. If the price relies on a possible repair, weigh that uncertainty first.
Compatibility and the value of parts
A donor unit needs the exact model or component code. A part that looks the same can differ in version, connector or firmware. Also check whether the part you're interested in has been tested itself.
Add diagnosis, labour, parts and transport. If you'll repair it yourself, consider the skills and tools needed. Damaged electrical devices or batteries may need a qualified specialist: a low price doesn't change the technical requirements.
Buy with a clear goal
On the lot page, look for known faults, missing parts and the test carried out. Don't buy an item meant for repair expecting to use it straight away. Decide how much you're prepared to invest even if the repair doesn't work out.