Most of locally made couches are made of pine; either recycled pallets, Wet of Saw (un-dried and un-graded timber), or KILN dried (a process which reduces the moisture of the wood); the latter being the correct product to be used when manufacturing couches.
Many cheap products are made using recycled pallet wood in most part of the couch. The main concern here is the thickness of the wood and therefore its strength; 19 instead of the 25cm, the minimum required to manufacture a long-lasting frame.
The use of un-dried wood (Wet of Saw), very common in the industry, is a serious concern as well. During its natural drying process, after the product was manufactured, the wood will be releasing its moisture, and mold will start forming on the fabric. It is obviously unhygienic but can also seriously damage the fabric, especially when using leather-like products such PU. The wood will also contract during this process, putting pressure on the joints of frame, weakening it, resulting in flimsy frame and squeaky noises eventually.
But more than the wood itself, the workmanship when manufacturing a couch frame is essential and participates largely in the lifespan of the final product. Glue should be used on all joints to ensure that the frame stays steady. But it takes time and is costly, so many factories don’t do it.
How can you know that the frame of the couch you are buying was properly manufactured and with the correct materials? If you buy it online, there is no way. If you physically see the product, you might be able to pick up a really poorly manufactured frame by touching and trying the product. But I am sorry to tell you than even an expert can’t tell for sure, once the product has been upholstered. The only way would be to remove the fabric; and that is obviously not a viable option.
And don’t ask the sales person… The person you should ask are the customers that purchased from that store in the past. Simply look at the store’s review on social platforms such as Google or Facebook; stores can’t fake it anymore. Read what customers have to say about the products they purchased.
Lastly, I would recommend you to be an informed and realistic buyer. I know and understand that everyone is looking out for a bargain. But after shopping around, you should have a fair idea of the “right” price point for the type of couch you are looking for. If it sounds too cheap, the chance might be that poor quality material were used.