When sourcing dog wheelchairs, the most critical factor is adjustability. Look for models with telescoping aluminum alloy frames that allow for height, length, and width adjustments to accommodate various breeds. The frame material should be aviation-grade aluminum to ensure it is lightweight yet durable, preventing additional strain on the dog's spine. For the wheels, EVA foam tires or pneumatic rubber wheels are preferred for their shock-absorption capabilities on uneven terrain. Additionally, ensure the harness system uses breathable sandwich mesh fabric and heavy-duty nylon webbing to prevent skin abrasion during prolonged use.