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At present the site does quite well on Google, will ads of this type jeopodize this?
Will this affect your visitor trust in you? I think that depends on the industry & market you target.
If you are being paid in advance I don't see a problem, monitor your traffic closely to see any patterns of behaviour (e.g. click on products, and exit - is a sure sign of unwanted ads not being tolerated).
If this is the case adjust the campaign accordingly.
If however, they are paying (per click) they will not suffer from a negative campaign thus you eat the negativity alone. A much higher risk is your case.
Personally - I would go for this unless the risk is equally divided between the players.