I have ordered clothing from Alibaba vendors and received everything fast with good communication. I charged all my purchases to my CC which has a good and fast refund policy if I have trouble with online purchases.
Maybe send this vendor a question regarding the arena. Ask if you can get just one set to test the quality. If they answer quickly, can comply to your request and seen to have good customer service you could order one set and put it on your credit card. Then wait and see. Call your CC company to ask their refund policy if you don’t know it already.
Many of these Alibaba companies are the original manufacturers for US based end sellers (who jack up the end price considerably).
The only problem may be that they need to ship in bulk in order to keep costs down. If this is the case suggest they send you a very small sample of the actual arena(maybe a cone or something) so you can see the quality. Also triple check on the exact measurements of the rails. (they’ll give them to you in centimeters.
The add seems to be for 5 sets, right? There is a description language problem here. Ask them if you can have one trial set or just a small sample and the shipping cost for that set or sample and take it from there. If they don’t get back or the answer is strange - then stay away.
Oh and let us know