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I have a passage, which will be shown to native speakers, and I am not allowed to make any mistake in grammar and style. If you can take a look at the sentences, which are in bold brown and give me your advice, I would appreciate that! I've posted the whole passage for context understanding. Thank you very much for your advice in advance!

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If you are in the business of leasing or renting real property for several years, you’ll have quite a database of tenants’ and owners’ contacts. Storing every detail of them can make them your clients again. Before the high season begins, send them a newsletter about a new option/discount/benefit for your web site visitors and include there a small paragraph about their family. For instance, tell them how cute were those twins John and Jack, who ‘refreshed’ your wall papers with their creative paintings the last year :- ), or how is that little dog Sparky, who misused your flower-beds and lawns :- )

Your tenants will appreciate your attention to them. You will make early reservations. You can hardly expect that at large vacation portals.

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If you have been in the business of leasing or renting real property for several years, you’ll have quite a database of tenant and owner contacts. Storing every detail about them can help you regain them as clients. Before the high season begins, send them a newsletter about a new option, discount or benefit for your website visitors and include a brief reference to their family. For instance, tell them how cute those twins, John and Jack, were, who ‘refreshed’ your wallpaper with their creative paintings last ask about their little dog year, or, Sparky, who misused your flowerbeds and lawn.
Your tenants will appreciate your attentions and will make early reservations. You could hardly expect that at large vacation portals.
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Just a suggestion: I think I would use "retain them as clients" rather than "regain them as clients".
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Hi Mister Micawber, I appreciate your help, thank you very much. I could not ask for more! [Y]
 Lil' Ruby Rose's reply was promoted to an answer.
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If you are in the business of leasing or renting real property for several years, you’ll have quite a database of tenants’ and owners’ contacts. Storing every detail of them can help to make them your clients again. Before the high season begins, send them a newsletter about a new option,discount and/or benefit to your web site visitors, and include a small paragraph about their family. For instance, tell them how cute those twins were, John and Jack, who ‘decorated' your wall paper with their creative paintings last year. Or you could tell them about that little dog Sparky, who misused your flower-beds and lawns.

Your tenants will appreciate the attention given to them. You will make early reservations. You can hardly expect that at large vacation portals.

Your english grammer is not too bad however i have made some amendments to you paragraph to make it more genuine. Also, what do you mean by 'vactation portals'? This phrase doesn't really make sense to me.

Kind regards, James.
Hi James, thank you for your comments. I think you are right, "vacation portals" should have sounded something like "vacation rental portals". Will it be better? [:^)]