Convert each side of a market to implied probability. For American odds, negative prices use |p| / (|p| + 100) and positive prices use 100 / (p + 100).
The excess over 100% is the margin, commonly called the vig or hold. A market pricing both sides at -110 sums to about 104.8%, so the hold is roughly 4.8%. That figure is arithmetic from the two prices you supply, not a claim about any operator.
Divide each implied probability by the total to get a fair-value estimate. This normalised number is what you would compare against an exchange quote or your own model.