Consider this

The most difficult part for the salesperson is to ......... potential customers of the usefulness of the product.
consider
convince
contract
confirm

If you want to get the best out of your sales force, they must believe in the product and be ......... enough to promote it vigorously.
inspired
invested
included
indebted

A ......... customer will always return to the same firm and buy again.
interested
encouraged
satisfactory
satisfied

That style of dress was once considered to be a ......... but now it is coming back into fashion.
fuss
fad
fidget
fun

One of the first things to do when you want to ......... a new product is to ascertain its potential demand.
maintain
master
market
muster

The main business interest at the moment is to watch the supermarkets ......... for the same clientele.
contrasting
competing
concerning
confusing

Our sales meetings were reduced to once a fortnight because the weekly meetings were not considered to be ......... enough.
productive
producing
produced
products

Her ability to ......... facts and figures quickly was the main reason for her rapid rise in the business.
consumer
consumption
consume
consuming

The success of our website is due to the fact that customers can ......... different prices for the same article.
continue
conclude
confer
compare

If you want to keep ......... with the latest developements in your field, you have to read the relevant magazines.
currant
current
currents
currently