Check frame quality: Put two hands on the whole sofa then shake and hang for a while from front to back or left to right. If you feel good, then the frame is fixed stable. Then talk to the sales, to open the fabric at the bottom for checking the wood panels. If there are not dirty, nor worm or dirty mark, no trunk or shining bits on the clean hardwood, then between bars are not connected by screws but with cutting matching then stick with glue, this is quality will be fine.
Check inside layers quality: Nowadays, most high class sofas had adopted cross netting with Nylon & springs combination, which add high density foam/ polyfoam & light foam. Such layers will be good strength to support your sitting and also turn back to normal seat height. Middle class sofa is made of MDF seat and back, then put middle density foam and polyfoam ontop, which will be harder and less strength for coming back to normal seat height.
Check fabri and sewing: If you want to buy leather sofa, then you have to choose the leather. Real leather sofa is devided into full leather sofa and semi-leather sofa. One leather sofa set will need 10 sets of cow leather, which is with high quality and good for air circulatioin and enviromental friendly. For countries over Europe and US, majority consumers had chosen full leather sofa. Semi-leather sofa will use PU leather or PVC to take replacement of cow leather on the seat and back or other places can be hidden, but for the touching area with human bodies, they will still use valueable cow leather, in order to reduce the costs of producing sofa and becomes more ecnomical friendly. Sofa cow leather normally devided into cow and buffalo leathers, which based on its layers as: first layer leather, 2nd. layer leather or 3rd.. Based on the place of origin, it will be domestic leather and imported leather. Among the imported leather, Italy and German 1st, layer leather is the best, which meet strict enviroment request and colour fastness good then good for machine handling, especially for tearing and anti-strength. Good quality fine sofa has to choose 1st.layer of cow leather.
When you buy leather sofa, the surface should be smooth without any marks and fine quality at hand. You can pick somewhere with your fingers then pull upwards, then you feel soft but gentle with strength. Then after your sitting on the sofa, wrinkles will fade or not that clear. And this will be first class fine leather.
When you buy fabric sofa, please pay more attention onto the seat and back should be flexible for seat and back and high class fabric sofa will have cotton covers inside, which can be easily changed and washable. Sofa fabric should be strong enough, which weights more than 300gram/sq2 will be durable then it should guarantee that scratches more than 12,000 times no balls pulling from the surface. Fabric can be devided into domestic or imported. Professional fabric suppliers from Europe and US will produce good quality fabric for sofa with little colour difference and colour fasteness is high. No wrong horizon thread appears, especially some high class fabric has special treatment on the surface to improve stain proof ability. Imported fabric also can prevent electronity and fire-retarded. When you buy the fabric sofa, you will need to choose fabric with good linning and no missing thread or thread heads, while hand feeling fine. Sewing will need to check as well to find out whether it is even and flat then with two hands pressing to see whether connection is tight and edge smooth.