[azalty]

source: eyal282 (https://forums.alliedmods.net/showthread.php?p=2617618)

// native int UsefulCommands_ApproximateClientRank(int client);

// returns approximate rank.
// Note: if client has no service medals, returns exact rank.
// Note: if client has one medal, returns exact rank ONLY if it's equipped.
// Note: if client has more than one medal, does not return exact rank, however if you wanna filter out newbies, will work fine.
// Note: if you kick a client based on his rank, you should ask him to temporarily equip a service medal if he reset his rank recently, and you should cache that his steam ID is an acceptable rank.
// Note: don't use this on Counter-Strike: Source lol.

public int Native_ApproximateClientRank(Handle caller, int numParams)
{	
	int PlayerResourceEnt = GetPlayerResourceEntity();
	
	int client = GetNativeCell(1);
	
	if(!IsClientInGame(client))
	{
		ThrowNativeError(SP_ERROR_NATIVE, "Invalid client index %i", client);
		return -1;
	}
	
	char sCoin[64], value, rank = GetEntProp(PlayerResourceEnt, Prop_Send, "m_nPersonaDataPublicLevel", _, client);
	IntToString(GetEntProp(PlayerResourceEnt, Prop_Send, "m_nActiveCoinRank", _, client), sCoin, sizeof(sCoin));
	
	if(rank == -1)
		rank = 0;
		
	if(GetTrieValue(Trie_CoinLevelValues, sCoin, value))
		rank += value;
	
	return rank;
}

The trie contains service medals' IDs I guess, just look at the original plugin