How do I keep Ender men out of my end shop

Cover the floor in double carpets - two layers of carpet. The endermen don't spawn on it, don't consider that a valid teleport destination and don't pathfind over it unless they happen to get there accidentally e.g. after dropping off ledges. Another option is waterlogged blocks - in particular, waterlogged upside-down stairs and slabs provide regular flat surface, and normal stairs can be shaped into fancy patterns of half block wide water channels.

Note full-top blocks like stairs or slabs will stop teleportation and pathfinding but not spawns - the endermen can still spawn on them (and sit there confused). Regular orientation stairs and carpets are spawn-proof. Also, transparent blocks like glass or bottom slabs are spawn-proof but don't do a thing against teleportation or pathfinding.