What tools do gambling or classifieds sites use to detect or know your using a vpn?
Thanks in advance.
Thru IP the owner can see your IP and if there's sudden changes on the activity especially with the location used and it frequently happen then they assume that that user is using VPN. There are some instances that they verify the real location of the user thru asking them to do KYC that's why some people found out located in restricted regions then got issue regarding on that situation.
Also try to read this
Web hosts and third parties, including Google, offer website operators free analytic data, including the locations of site visitors. That information can be useful in many ways, even for small businesses. For example, a residential roofing contractor in a suburb of Toronto might want to analyze its website traffic to measure the effectiveness of its local advertising. If the site has visitors from Germany and New Zealand, the data becomes meaningless. If a high percentage of traffic comes from far-flung places, the business owner can deduce that most of those visitors are using VPNs.
Source
https://www.comparitech.com/blog/vpn-privacy/how-easy-is-it-to-detect-a-vpn-being-used/For whatever reason you have don't use VPN in a casino since we are dealing money with them and maybe there might be an issue arise if we insist to use especially if the casino is not a VPN friendly.