The help we provide as counter people is dependent on good information coming across the counter to us, as well as the information from our parts vendors, and our own ability. “Garbage in, garbage out” is unfortunately a stark reality, and we are likely to receive the blame regardless of who was actually at fault. The best option is to politely explain the situation: you are unable to accurately catalog the part without additional information, but you would be happy to pick up where you left off once you get that information. Then make sure you follow through when they return. If they insist on ordering “maybe” parts, explain your return policies thoroughly.