If your property is being marketed to the investment market, then yes the increase current rent may 'trick' buyers into paying more (by increasing the perceived yield of the property). Like Dazz said, if they do their homework they will see straight through it, but some will not do their homework.
Is it ethical??.. No, I don't think inflating rent to raise your selling price is ethical. Unless you are raising it to a point which would be considered market value.
In saying this, some owners in Commercial offer rent free periods, cash incentives at beginning of lease, construct fit out for tenant, hardstand additional yard area for them, improve building, add power etc etc to boost the rental up, which looks better to the owners' banks and any potential buyers in the case that they sell. Again, buyers should do their research to discern whether the tenants are paying current market rates, but if they don't, then this can be a trap.
I recommend regular market reviews though in any case. There are plenty of owners out there with rents significantly below market rent due to bad management or laziness. One of my clients just sold a 3bdr house on 5 acres near Penrith for $800k. Not sure what market rent is ($600-800/wk?), but his nephew had leased it for the last 15 years for $100/week
Luckily my client has enough property in his portfolio that this didn't bother him in the slightest