What are the low-price traps in whole-house customization? Where do add-on charges usually come from?

Common add-on charges are concentrated in a few areas: ① whether visible end panels, closing strips, and top lines and kickboards are priced separately; ② whether extra-height cabinets, irregular-shaped cabinets, and curved components are charged separately; ③ whether accessories such as drawers, pull-out baskets, trouser racks, light strips, and dressing mirrors are included in the quote; ④ whether worktop cutouts (sink, cooktop, built-in appliances) are charged extra; ⑤ whether transport, carrying upstairs, installation, and removal of existing cabinets are charged separately. The way to judge is straightforward: have them list these items one by one on the quotation, mark each as "included/not included," and then compare the total amount of different proposals rather than comparing only the initial quote.